Does Connecticut have income tax? Yes, Connecticut does have a state income tax. This guide from income-partners.net breaks down everything you need to know about Connecticut’s income tax system, from who needs to file to recent legislative changes that could impact your tax liability. Partnering with the right experts can help you navigate these complexities and potentially increase your income. Let’s explore Connecticut income tax.
1. Who Must File a Connecticut Resident Income Tax Return?
Who needs to file a Connecticut income tax return? You must file a Connecticut resident income tax return if you meet specific criteria, regardless of whether you are a business owner, investor, marketing expert, or someone seeking new business opportunities. Understanding these requirements is essential for anyone looking to succeed in Connecticut’s dynamic business environment.
You must file a Connecticut resident income tax return if you were a resident for the entire year and any of the following is true for the 2024 taxable year:
- You had Connecticut income tax withheld;
- You made estimated tax payments to Connecticut or a payment with Form CT‑1040 EXT;
- You had a PE Tax Credit;
- You meet the Gross Income Test;
- You had a federal alternative minimum tax liability; or
- You are claiming the Connecticut earned income tax credit (CT EITC).
If none of the above apply, do not file a Connecticut resident income tax return.
2. What are the Key Changes to Connecticut Income Tax Laws for 2024?
What are the major changes in Connecticut tax laws? Several legislative changes impact Connecticut income tax for the 2024 taxable year, potentially affecting your financial strategies and business decisions. Staying informed about these updates is crucial for effective income management.
- Reduction in certain income tax rates: The 3% rate on the first $10,000 earned by unmarried individuals and the first $20,000 by couples will decrease to 2%. The 5% rate on the next $40,000 earned by unmarried individuals and the next $80,000 earned by couples will decrease to 4.5%. These benefits will be capped at unmarried individual filers who earn $150,000 and couples who earn $300,000. This legislation is effective from passage and applicable to taxable years beginning on or after January 1, 2024.
- Historic Homes Rehabilitation Tax Credit: The credit allowed under Conn. Gen. Stat. § 10-416 may claimed against the taxes set forth in chapter 207, 208, 209, 210, 211 or 212 for vouchers issued prior to January 1, 2024 and against the taxes set forth in chapter 207, 208, 208a, 209, 210, 211, 212 or 229 for vouchers issued after January 1, 2024. The legislation also makes changes to the carryforward provisions relative to said credit. The legislation is effective July 1, 2024, and applicable to taxable and income years commencing on or after January 1, 2024.
- Withholding provisions relative to pension and annuity distributions: Payers of distributions from a profit-sharing plan, a stock bonus, a deferred compensation plan, an individual retirement arrangement, an endowment or a life insurance contract, or of pension payments or annuity distributions are no longer required to withhold on payments from such accounts. That said, a recipient may still request that Connecticut income tax be withheld from such distributions. Said requests must be made in accordance with applicable regulations. With regard to lump sum payments, payers remain obligated to withhold from qualified distributions if the distribution is in excess of $5,000 or is more than 50% of the balance of the account from which such distribution is being made from. The legislation is effective January 1, 2025, and applicable to taxable years commencing on or after January 1, 2025.
- New subtraction modification for payments received from the Fallen Officer Fund: Legislation provides for a subtraction modification for payments received from the Fallen Officer Fund. The legislation is effective from passage and applicable to taxable years commencing on or after January 1, 2024.
- Subtraction modification for contributions made by taxpayers into ABLE accounts: Legislation creates a subtraction modification for contributions to an ABLE account. The subtraction modification shall not exceed $5,000 per taxable year for single filers and not more than $10,000 per taxable year for joint filers. The legislation is effective January 1, 2024, and applicable to income years and taxable years commencing on or after January 1, 2024.
- New Tax Credit for pre- and post-Broadway productions and live theatrical tours: Legislation establishes a new tax credit for production companies of eligible pre- and post-Broadway productions and live theatrical tours performed at qualified facilities in Connecticut. The legislation specifies the taxes against which the credit can be applied and caps the total amount of these tax credits allowed to $2.5 million per fiscal year. This legislation is effective January 1, 2024, and applicable to income and taxable years commencing on or after January 1, 2024.
- New Tax Credit for youth development organization: Legislation authorizes a new tax credit for cash contributions made to a youth development organization to fund programs such as after-school tutoring, mentoring programs and workforce preparedness training. The credit is only available for income or taxable years commencing on or after January 1, 2024, and prior to January 1, 2026. This legislation is effective January 1, 2024.
- New Tax Credit for contributions made by taxpayers into ABLE accounts: Legislation authorizes a new tax credit for contributions made by taxpayers into the ABLE accounts of employees who are employed by such taxpayers. The legislation specifies the taxes against which the credit can be applied and is effective January 1, 2024, and applicable to income years or taxable years commencing on or after January 1, 2024.
- Authorization to Receive Health Coverage Information from Access Health CT: Legislation allows the Department of Revenue Services to share tax return information with Access Health CT with taxpayer authorization.
By checking the box on Form CT-1040, Connecticut Resident Income Tax Return, you authorize the Department of Revenue Services to transmit certain demographic information about you and your household to Access Health CT. This election authorizes Access Health CT to contact you with information about health coverage options and financial assistance that may be available to you.
3. What is the Gross Income Test for Connecticut Income Tax?
What is the Connecticut gross income test? The gross income test determines whether you are required to file a Connecticut income tax return, regardless of your profession or business ventures. Understanding this test is key to ensuring compliance and exploring opportunities to increase your income through strategic partnerships.
Gross income means all income you received in the form of money, goods, property, services not exempt from federal income tax, and any additions to income required to be reported on Form CT‑1040, Schedule 1.
Gross income includes income from all sources within Connecticut and outside of Connecticut. Gross income includes but is not limited to:
- Compensation for services, including wages, fees, commissions, taxable fringe benefits, and similar items;
- Gross income from a business;
- Capital gains;
- Interest and dividends;
- Gross rental income;
- Gambling winnings;
- Alimony;
- Taxable pensions and annuities;
- Prizes and awards;
- Your share of income from partnerships, S corporations, estates, or trusts;
- IRA distributions;
- Unemployment compensation;
- Federally taxable Social Security benefits; and
- Federally taxable disability benefits.
You must file a Connecticut income tax return if your gross income for the 2024 taxable year exceeds:
- $12,000 and you are married filing separately;
- $15,000 and you are filing single;
- $19,000 and you are filing head of household; or
- $24,000 and you are married filing jointly or qualifying surviving spouse.
3.1. Examples of the Gross Income Test
Here are some examples to clarify the gross income test for a Connecticut resident:
Example 1: Your only income is from a sole proprietorship and you file federal Form 1040 reporting the following on Schedule C:
| Gross Income | $100,000 |
|---|---|
| Expenses | ($92,000) |
| Net Income | $8,000 |
Because the gross income of $100,000 exceeds the minimum requirement, you must file a Connecticut income tax return.
Example 2: You received $8,000 in federally nontaxable Social Security benefits and $11,000 in interest income. Since nontaxable Social Security benefits are not included in gross income, you do not have to file a Connecticut income tax return unless Connecticut tax was withheld or estimated tax payments were made.
Example 3: You are a single individual. You received $15,000 in wage income and $1,000 in federally-exempt interest from California state bonds. Your gross income (federal adjusted gross income with any additions to income from Form CT‑1040, Schedule 1, Line 31, Interest on state and local government obligations other than Connecticut) is $16,000. Therefore, you must file a Connecticut income tax return.
4. What are the Free Filing Options for Connecticut Resident Individuals?
How can I file my Connecticut income tax for free? Connecticut offers several free filing options for resident individuals, ensuring accessibility and convenience for all taxpayers, including entrepreneurs, investors, and marketing professionals. These options can save you money, which can then be reinvested into growing your income and business ventures.
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myconneCT: In order to file your return, you must be able to create a username and log into myconneCT. To create a username, you will need to authenticate your information with one of the following:
- The Federal Adjusted Gross income from one of your three most recently filed Connecticut income tax returns;
- A valid Connecticut driver’s license or Connecticut non-driver ID;
Please be prepared to submit any of the following forms as attachments. If applicable, you must include them in your filing: - Form CT 1040 CRC, Claim of Right Credit;
- Form CT 19IT, Title 19 Status Release Form;
- Form 1310, Statement of Person Claiming Refund Due a Deceased Taxpayer;
- Form CT-8379, Nonobligated Spouse Claim;
- Form CT-2210, Underpayment of Estimated Income Tax by Individuals, Trusts, and Estates;
- Other (e.g., copy of your federal return, other jurisdiction etc.)
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Modernized e‑file (MeF): Submit your return electronically through third party software either through your paid preparer or online or through commercially available software. If you have a balance due, submit your payment electronically. If you choose to mail in your balance due, do not send a paper copy of your electronically filed return with the payment. Simply mail Form CT 1040V, Connecticut Electronic Filing Payment Voucher, with your check or money order.
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Complete Your State Return with Direct File: Connecticut (CT) partnered with the IRS to give you an option for filing your federal and state tax returns for free.
Direct File will open January 27, 2025, for CT tax return submissions.
Find out if Direct File is right for you.Check eligibility now (State | Direct File | Internal Revenue Service)
The use of software will help aid you to prepare and file your return easily and accurately. You will also be provided with a confirmation of receipt for your peace of mind.
5. What Special Information Applies to Nonresident Aliens in Connecticut?
What if I am a nonresident alien in Connecticut? Nonresident aliens have specific filing requirements for Connecticut income tax. Understanding these rules is essential for compliance and for leveraging potential business and investment opportunities in Connecticut.
If you are a nonresident alien, you must file a Connecticut income tax return if you meet the requirements of Who Must File a Connecticut Resident Return. In determining whether you meet the gross income test, you must take into account any income not subject to federal income tax under an income tax treaty between the United States and the country of which you are a citizen or resident. Income tax treaty provisions are disregarded for Connecticut income tax purposes. Any treaty income you report on federal Form 1040NR and not subject to federal income tax must be added to your federal adjusted gross income. See Form CT-1040, Schedule 1, Line 37, or Form CT-1040NR/PY, Schedule 1, Line 39.
If you do not have and are not eligible for a Social Security Number (SSN), you must obtain an Individual Taxpayer Identification Number (ITIN) from the IRS and enter it in the space provided for an SSN.
You must have applied for and been issued an ITIN before you file your income tax return. However, if you have not received your ITIN by April 15, file your return without the ITIN, enter Applied for or NRA in the SSN field, pay the tax due, and attach a copy of federal Form W‑7, Application for IRS Individual Taxpayer Identification Number. DRS will contact you upon receipt of your return and will hold your return until you receive your ITIN and you forward the information to us. DRS cannot process your return until we receive the ITIN.
A married nonresident alien may not file a joint Connecticut income tax return unless the nonresident alien is married to a citizen or resident of the United States and they have made an election to file a joint federal income tax return and they do, in fact, file a joint federal income tax return. Any married individual filing federal Form 1040NR is not eligible to file a joint federal income tax return or a joint Connecticut income tax return and must file a Connecticut income tax return as filing separately.
6. How Does Connecticut Define Resident, Part-Year Resident, and Nonresident Status?
What are the different residency statuses in Connecticut? Understanding the definitions of resident, part-year resident, and nonresident is crucial for determining your filing requirements and tax obligations in Connecticut. These distinctions are particularly important for those looking to establish or expand their business operations in the state.
The following terms are used in this section:
Domicile (permanent legal residence) is the place you intend to have as your permanent home. It is the place you intend to return to whenever you are away. You can have only one domicile although you may have more than one place to live. Your domicile does not change until you move to a new location and definitely intend to make your permanent home there. If you move to a new location but intend to stay there only for a limited time (no matter how long), your domicile does not change. This also applies if you are working in a foreign country.
Permanent place of abode is a residence (a building or structure where a person can live) that you permanently maintain, whether or not you own it, and generally includes a residence owned by or leased to your spouse. A place of abode is not permanent if it is maintained only during a temporary stay for the accomplishment of a particular purpose.
6.1. Resident
You are a resident for the 2024 taxable year if:
- Connecticut was your domicile (permanent legal residence) for the entire 2024 taxable year; or
- You were not domiciled in Connecticut, but you maintained a permanent place of abode in Connecticut during the entire 2024 taxable year and spent a total of more than 183 days in Connecticut during the 2024 taxable year.
Nonresident aliens who meet either of these conditions are considered Connecticut residents even if federal Form 1040NR is filed for federal income tax purposes. See also Special Rules for Married Individuals and Special Information for Nonresident Aliens.
If you are a resident and you meet the requirements for Who Must File a Connecticut Resident Return for the taxable year, you must file Form CT-1040, Connecticut Resident Income Tax Return.
6.2. Part-Year Resident
You are a part-year resident for the 2024 taxable year if you changed your permanent legal residence by moving into or out of Connecticut during the 2024 taxable year. If you are a part-year resident, you may not elect to be treated as a resident individual.
If you are a part-year resident and you meet the requirements for Who Must File Form CT-1040NR/PY for the 2024 taxable year, you must file Form CT-1040NR/PY, Connecticut Nonresident and Part-Year Resident Income Tax Return.
6.3. Nonresident
You are a nonresident for the 2024 taxable year if you are neither a resident nor a part-year resident for the 2024 taxable year.
If you are a nonresident and you meet the requirements for Who Must File Form CT‑1040NR/PY for the 2024 taxable year, you must file Form CT‑1040NR/PY.
If you meet all of the conditions in Group A or Group B, you may be treated as a nonresident for 2024 even if your domicile was Connecticut.
Group A
- You did not maintain a permanent place of abode in Connecticut for the entire 2024 taxable year;
- You maintained a permanent place of abode outside of Connecticut for the entire 2024 taxable year; and
- You spent not more than 30 days in the aggregate in Connecticut during the 2024 taxable year.
Group B
- You were in a foreign country for at least 450 days during any period of 548 consecutive days;
- During this period of 548 consecutive days, you did not spend more than 90 days in Connecticut and you did not maintain a permanent place of abode in Connecticut at which your spouse (unless legally separated) or minor children spent more than 90 days; and
- During the nonresident portion of the taxable year in which the 548‑day period begins, and during the nonresident portion of the taxable year in which the 548‑day period ends, you were present in Connecticut for no more than the number of days that bears the same ratio to 90 as the number of days in the portion of the taxable year bears to 548. See the calculation below:
| Number of days in the nonresident portion x 90 = Maximum days allowed in Connecticut 548 |
|---|
See Special Notice 2000(17), 2000 Legislation Affecting the Connecticut Income Tax.
7. What are the Filing Requirements for Military Personnel?
How does military service affect Connecticut income tax? Military personnel and their spouses have specific Connecticut income tax filing requirements, particularly if they claim Connecticut as their state of residence but are stationed elsewhere. Understanding these rules is essential for military families looking to optimize their financial strategies and explore business opportunities.
Military personnel and their spouses who claim Connecticut as their state of residence but are stationed elsewhere are subject to Connecticut income tax.
If you enlisted in the military service as a Connecticut resident and have not established a new domicile (permanent legal residence) elsewhere, you are required to file a resident income tax return unless you meet all of the conditions in Group A or Group B for being treated as a nonresident. See Resident, Part‑Year Resident, or Nonresident above.
If your permanent home (domicile) was outside Connecticut when you entered the military, you do not become a Connecticut resident because you are stationed and live in Connecticut. As a nonresident, your military pay is not subject to Connecticut income tax. However, income you receive from Connecticut sources while you are a nonresident may be subject to Connecticut income tax. See the instructions for a Nonresident. See Example, below.
Example: Jill is a resident of Florida. She enlisted in the Navy in Florida and was stationed in Groton, Connecticut. She earned $38,000 in military pay.
If Jill had no other income . . .
Since Jill resided and enlisted in Florida, she is considered a resident of Florida and does not have to file a Connecticut return. Military personnel are residents of the state in which they resided when they enlisted.
If Jill had a part-time job in Connecticut . . .
Her Connecticut-sourced income from nonmilitary employment is taxable. Jill must file Form CT‑1040NR/PY to report the income.
7.1. Combat Zone
The income tax return of any individual in the U.S. Armed Forces serving in a combat zone or injured and hospitalized while serving in a combat zone is due 180 days after returning. There will be no penalty or interest charged. For any individual who dies while on active duty in a combat zone or as a result of injuries received in a combat zone, no income tax or return is due for the year of death or for any prior taxable year ending on or after the first day serving in a combat zone. If any tax was previously paid for those years, the tax will be refunded to the legal representative of the estate or to the surviving spouse upon the filing of a return on behalf of the decedent. In filing the return on behalf of the decedent, the legal representative or the surviving spouse should enter zero tax due and attach a statement to the return along with a copy of the death certificate.
Combat zone is an area designated by an Executive Order from the President of the United States as areas in which the U.S. Armed Forces are engaging or have engaged in combat. A combat zone also includes an area designated by the federal government as a qualified hazardous duty area.
Spouses of military personnel and civilians supporting the military in a combat zone region who are away from their permanent duty stations, but are not within the designated combat zone, are also eligible for the 180 day extension.
Individuals requesting an extension under combat zone provisions should print both the name of the combat zone and the operation they served with at the top of their Connecticut tax return. This is the same combat zone or operation name provided on their federal income tax return. See Informational Publication 2019(5), Connecticut Income Tax Information for Armed Forces Personnel and Veterans.
8. How is Connecticut Adjusted Gross Income Calculated?
What is Connecticut Adjusted Gross Income? Connecticut adjusted gross income (CT AGI) is a key figure in determining your Connecticut income tax liability, affecting everyone from business owners to marketing experts. Knowing how it’s calculated is essential for accurate tax planning and maximizing your income potential through strategic partnerships.
Connecticut adjusted gross income is your federal adjusted gross income as properly reported on federal Form 1040, Line 11, or federal Form 1040-SR, Line 11, and any Connecticut modifications required to be reported on Form CT-1040, Schedule 1.
9. How Can I Request an Extension of Time to File My Connecticut Income Tax Return?
How do I request a Connecticut tax extension? Requesting an extension of time to file your Connecticut income tax return allows you more time to prepare and file accurately, which is particularly useful for entrepreneurs and investors managing multiple financial streams.
Extension of Time to File
To request an extension of time to file your return, you must file Form CT‑1040 EXT, Application for Extension of Time to File Connecticut Income Tax Return for Individuals and pay all the tax you expect to owe on or before the due date.
Visit portal.ct.gov/DRS-myconneCT to file your extension electronically.
Form CT‑1040 EXT extends only the time to file your return; it does not extend the time to pay your tax due. See Interest and Penalties if you do not pay all the tax due with your extension request.
You do not need to file Form CT‑1040 EXT if you:
- Have requested an extension of time to file your 2024 federal income tax return and you expect to owe no additional Connecticut income tax for the 2024 taxable year after taking into account any Connecticut income tax withheld from your wages, any Connecticut income tax payments you have made, and any Pass‑Through Entity Tax Credit (PE Tax Credit) you are allowed to claim; or
- Pay your expected 2024 Connecticut income tax due using a credit card on or before the due date.
You must file Form CT‑1040 EXT if you:
- Did not request an extension of time to file your federal income tax return, but you are requesting an extension of time to file your Connecticut income tax return; or
- Have requested an extension of time to file your federal income tax return but you expect to owe additional Connecticut income tax for 2024 and wish to submit a payment with Form CT‑1040 EXT.
If you file an extension request with a payment after the due date, generally April 15, DRS will deny your extension request.
9.1. U.S. Citizens Living Abroad
If you are a U.S. citizen or resident living outside the United States and Puerto Rico, or if you are in the armed forces of the United States serving outside the United States and Puerto Rico and are unable to file a Connecticut income tax return on time, you must file Form CT‑1040 EXT. You must also pay the amount of tax due on or before the original due date of the return.
Include with Form CT‑1040 EXT a statement that you are a U.S. citizen or resident living outside the United States and Puerto Rico, or in the armed forces of the United States serving outside the United States and Puerto Rico, and that you qualify for a federal automatic extension. If your application is approved, the due date is extended for six months.
If you received a federal extension of time to file beyond six months, to qualify for the federal foreign earned income exclusion and for the foreign housing exclusion or deduction, you may file your Connecticut return using the federal extension due date. Submit a copy of the approved federal Form 2350, Application for Extension of Time to File U.S. Income Tax Return, by attaching it to the front of your Form CT‑1040.
9.2. Extension of Time to Pay
You may be eligible for a six-month extension of time to pay the tax due if you can show that paying the tax by the due date will cause undue hardship. You may request an extension by filing Form CT-1127, Application for Extension of Time for Payment of Income Tax, on or before the due date of the original return.
Attach Form CT-1127 to the front of Form CT-1040 or Form CT-1040 EXT and send it on or before the due date. As evidence of the need for extension, you must attach:
- An explanation of why you cannot borrow money to pay the tax due;
- A statement of your assets and liabilities; and
- An itemized list of your receipts and disbursements for the preceding three months.
If an extension of time to pay is granted and you pay all the tax due in full by the end of the extension period, a penalty will not be imposed. However, interest will accrue on any unpaid tax from the original due date. You should make payments as soon as possible to reduce the interest you would otherwise owe.
10. How Do Estimated Tax Payments Work in Connecticut?
How do I make estimated tax payments in Connecticut? Making estimated tax payments is essential for those whose income isn’t subject to withholding, such as entrepreneurs and investors. Understanding these requirements can help you avoid penalties and effectively manage your financial obligations.
You must make estimated income tax payments if:
- Your Connecticut income tax, after taking into account your Connecticut tax withheld, and any Pass‑Through Entity Tax Credit (PE Tax Credit) you are allowed to claim, is $1,000 or more; and
- You expect your Connecticut income tax withheld (including any PE Tax Credit) to be less than your required annual payment for the 2025 taxable year.
Your required annual payment for the 2025 taxable year is the lesser of:
- 90% of the income tax shown on your 2025 Connecticut income tax return; or
- 100% of the income tax shown on your 2024 Connecticut income tax return, if you filed a 2024 Connecticut income tax return that covered a 12‑month period.
You do not have to make estimated income tax payments if:
- You were a Connecticut resident during the 2024 taxable year, and you did not file a 2024 income tax return because you had no Connecticut income tax liability; or
- You were a nonresident or part-year resident with Connecticut-sourced income during the 2024 taxable year and you did not file a 2024 income tax return because you had no Connecticut income tax liability.
If you were a nonresident or part-year resident and you did not have Connecticut-sourced income during the 2024 taxable year, your required annual payment is 90% of the income tax shown on your 2024 Connecticut income tax return.
10.1. Annualized Income Installment Method
If your income varies throughout the year, you may be able to reduce or eliminate the amount of your estimated tax payment for one or more periods by using the annualized income installment method. See Informational Publication 2018(11), A Guide to Calculating Your Annualized Estimated Income Tax Installments and Worksheet CT‑1040 AES.
10.2. Filing Form CT-1040ES
You may file and pay your 2025 Connecticut estimated tax using myconneCT. You may also make your payments by credit card. Visit the DRS website at portal.ct.gov/DRS-myconneCT for more information.
Use Form CT‑1040ES, Estimated Connecticut Income Tax Payment Coupon for Individuals, to make estimated Connecticut income tax payments for 2025 by mail. If you made estimated tax payments by mail in 2024, you will automatically receive coupons for the 2025 taxable year in mid‑January. They will be preprinted with your name, address, and the last four digits of the SSN. To ensure your payments are properly credited, use the preprinted coupons.
If you did not make estimated tax payments in 2024, use Form CT‑1040ES to make your first estimated income tax payment. Form CT‑1040ES is available on the DRS website at portal.ct.gov/DRS. If you file this form, additional preprinted coupons will be mailed to you.
To avoid making estimated tax payments, you may request that your employer or payer withhold additional amounts from your wages, pension, or annuity to cover the taxes on other income. You can make this change by giving your employer or payer a revised Form CT‑W4, Employee’s Withholding Certificate or Form CT‑W4P, Withholding Certificate for Pension or Annuity Payments. For help in determining the correct amount of Connecticut withholding be withheld from your income, see Informational Publication 2024(7), Is My Connecticut Withholding Correct?
| 2025 Estimated Tax Due Dates Due dates of installments and the amount of required payments for 2024 calendar year taxpayer are: |
|---|
| April 15, 2025 |
| June 15, 2025 |
| September 15, 2025 |
| January 15, 2026 |
| An estimate is considered timely filed if received on or before the due date, or it the date shown by the U.S Postal Service cancellation mark is on or before the due date. Taxpayers who report on other than a calendar year basis should use their federal estimated tax installment due dates. If the due date falls on a Saturday, Sunday, or legal holiday, the return will be considered timely if filed by the next business day. |
10.3. Special Rules for Farmers and Fishermen
If you are a farmer or fisherman (as defined in IRC § 6654(i)(2)) who is required to make estimated income tax payments, you must make only one payment. Your payment is due on or before January 15, 2026, for the 2025 taxable year. The required installment is the lesser of 66 2/3% of the income tax shown on your 2025 Connecticut income tax return or 100% of the income tax shown on your 2024 Connecticut income tax return.
If you file a 2025 Connecticut income tax return on or before March 1, 2026, and pay in full the amount computed on the return as payable on or before that date, you will not be charged interest for underpayment of estimated tax.
Farmers or fishermen who use these special rules must complete and attach Form CT‑2210, Underpayment of Estimated Tax by Individuals, Trusts, and Estates, to their Connecticut income tax return to avoid being billed for interest on the underpayment of estimated income tax. Check Box D of Form CT‑2210, Part 1, and the box for Form CT‑2210 on the front of Form CT‑1040NR/PY. See Informational Publication 2021(2), Farmer’s Guide to Sales and Use Taxes, Motor Vehicle Fuels Tax, Estimated Income Tax, and Withholding Tax, or Informational Publication 2021(4), Commercial Fisherman’s Guide to Sales and Use Taxes and Estimated Income Tax.
10.4. Filing Form CT-2210
Use Form CT‑2210 to calculate interest on the underpayment of estimated tax. Form CT‑2210 and detailed instructions are available from DRS. However, this is a complex form, and you may prefer to have DRS calculate the interest. If so, do not file Form CT‑2210 and DRS will send you a bill.
10.5. Interest on Underpayment of Estimated Tax
You may be charged interest if you did not pay enough tax through withholding or estimated payments, or both, by any installment due date, or if any PE Tax Credit reported to you on Schedule CT K‑1, Part 4, Line 1, or Schedule CT‑1041 K‑1, Part 4, Line 1, is not sufficient to cover your tax liability by the installment due date. This is true even if you are due a refund when you file your tax return. Interest is calculated separately for each installment. Therefore, you may owe interest for an earlier installment even if you paid enough tax later to make up the underpayment. Interest at 1% per month or fraction of a month will be added to the tax due until the earlier of April 15, 2025, or the date on which the underpayment is paid.
If you file a 2024 Connecticut income tax return on or before January 31, 2025, and pay in full the amount computed on the return as payable on or before that date, you will not be charged interest for failing to make the estimated payment due January 15, 2025.
Farmers or fishermen: see Special Rules for Farmers and Fishermen
