To fill out CT-1040, start with the federal adjusted gross income from your completed federal return, apply Connecticut’s additions and subtractions on Schedule 1, run the resulting Connecticut taxable income through the state’s seven-bracket rate schedule, subtract credits such as the property tax credit and the Connecticut earned income tax credit, add any use tax you owe, and file through the myconneCT portal or by mail to the Department of Revenue Services in Hartford by April 15.
Do You File CT-1040 in the First Place?
CT-1040 is the resident return. Connecticut treats you as a resident if you were domiciled in the state for the full tax year, or if you kept a permanent place of abode here and spent more than 183 days in Connecticut during the year.1Justia. Connecticut Code 12-701 – Definitions. Regulations. Active-duty military members not domiciled in Connecticut are exempt from the 183-day rule.
If you moved into or out of Connecticut during the year, or you live elsewhere but earned Connecticut-source income, you use Form CT-1040NR/PY instead. Connecticut has no reciprocal agreements with its neighbors, so a New York or Massachusetts resident who works in Connecticut still owes Connecticut tax on that income.
Even as a resident, you only need to file when your gross income from all non-exempt sources reaches the floor for your filing status:
- Single: $15,000
- Married filing separately: $12,000
- Head of household: $19,000
- Married filing jointly: $24,000
File anyway if you expect a refund. The money doesn’t come without a return on record.2Connecticut State Department of Revenue Services. Form CT-1040 Connecticut Resident Income Tax Return Instructions
What to Have in Front of You
Finish your federal 1040 first. Every number on the CT-1040 flows from it. Then pull together:
- All W-2s and 1099s for the year
- Social Security numbers for you, your spouse, and any dependents
- Property tax bills for your Connecticut home and motor vehicles, if you paid any during the year
- Records of estimated payments made through myconneCT or paper CT-1040ES vouchers
- Receipts for taxable out-of-state or online purchases where no Connecticut sales tax was collected
- Any Schedule CT K-1s you received from Connecticut partnerships or S-corporations
Line 1: Federal Adjusted Gross Income
Line 1 of CT-1040 is your federal adjusted gross income, copied exactly from line 11 of your federal 1040. If that number isn’t final, stop and finish the federal return before going further. Nothing on the Connecticut form will come out right otherwise.
Connecticut Modifications on Schedule 1
Connecticut doesn’t accept federal AGI as the final measure of what it can tax. Schedule 1 walks you through additions and subtractions that convert federal AGI into Connecticut AGI.1Justia. Connecticut Code 12-701 – Definitions. Regulations.
Typical additions include interest on municipal bonds issued by other states, which is federally tax-free but taxable in Connecticut. Typical subtractions include federally taxable Social Security benefits and interest on U.S. government obligations such as Treasury bonds, both of which Connecticut exempts. Work through every line of Schedule 1 that applies, then carry the net Connecticut AGI back to the main form.
Applying the Tax Rate Schedule
Connecticut’s income tax uses seven brackets. For single filers and those married filing separately, the 2025 brackets are:
- 2% on the first $10,000
- 4.5% from $10,001 to $50,000
- 5.5% from $50,001 to $100,000
- 6% from $100,001 to $200,000
- 6.5% from $200,001 to $250,000
- 6.9% from $250,001 to $500,000
- 6.99% above $500,000
For married couples filing jointly, the bracket thresholds are roughly double. The 2% rate covers the first $20,000, the 4.5% rate runs up to $100,000, and the top 6.99% rate begins above $1,000,000.3Connecticut General Assembly. Connecticut Income Tax Rates and Brackets Since 1991 The reduced rates in the bottom two brackets phase out for single filers above $105,000 of Connecticut AGI and joint filers above $210,000, so higher earners effectively pay a flatter schedule.
Credits That Reduce What You Owe
Once you have an initial tax figure, apply the credits.
The property tax credit is worth up to $300 against your tax for qualifying property tax paid during the year on a primary Connecticut residence, a privately owned or leased motor vehicle, or both. Only payments actually due and paid during the tax year count; late payments and the interest or fees attached to them don’t. Single filers and heads of household can include one motor vehicle; joint filers can include two.4Department of Revenue Services. Form CT-1040 Connecticut Resident Income Tax Return Instructions
The Connecticut earned income tax credit equals 40% of the federal earned income credit you claimed.5Justia. Connecticut Code 12-704e – Earned Income Tax Credit There’s no separate eligibility test. If you qualified federally, carry the federal credit over and multiply by 0.40. If you filed a joint federal return but must file separately in Connecticut, prorate the credit based on your share of the joint federal AGI.
If you’re a partner or S-corporation shareholder in an entity that elected to pay the Connecticut pass-through entity tax, you can claim a credit for your share. The amount comes from the Schedule CT K-1 the entity issues you.6Connecticut State Department of Revenue Services. Pass-Through Entity Tax Information
The Use Tax Line
CT-1040 includes a line for individual use tax. If you bought taxable goods from an out-of-state retailer, usually online, and didn’t pay Connecticut sales tax at the time, you owe use tax at the same rate.7Connecticut State Department of Revenue Services. Individual Use Tax Information If another state’s sales tax was collected on the purchase, you only owe the difference. Enter zero if nothing applies. Leaving the line blank when you do owe exposes you to the same penalties as underpaying income tax.
Filing the Completed Return
DRS encourages electronic filing through the myconneCT portal or through commercial tax software that supports Connecticut. E-filing confirms receipt immediately and moves refunds faster than paper.
If you mail a paper return, the address depends on whether money is changing hands:
- Refund or no payment due: Department of Revenue Services, PO Box 2976, Hartford CT 06104-2976
- Payment enclosed: Department of Revenue Services, PO Box 2977, Hartford CT 06104-2977
Attach Form CT-1040V as a payment voucher when you send a check or money order with the return.8Connecticut State Department of Revenue Services. DRS Forms, Instructions, and Assistance
If You Need More Time to File
Form CT-1040 EXT buys a six-month filing extension, pushing the deadline to October 15. You must file the extension by the original April 15 due date and pay any tax you expect to owe with it, because the extension covers filing, not payment.9Department of Revenue Services. Form CT-1040 EXT Application for Extension of Time to File Connecticut Income Tax Return If you expect no additional Connecticut tax after withholding and estimated payments, and you’ve already requested a federal extension, DRS grants the state extension automatically. You hear from them only if it’s denied.
Paying, Penalties, and Refunds
Pay electronically through myconneCT by bank transfer, or mail a check or money order with CT-1040V. Payment is due April 15 whether or not you extended the filing deadline.
Miss the filing deadline without an extension and DRS will estimate your tax from available records and add a penalty of 10% of the tax due or $50, whichever is greater. File on time but pay short, and the penalty is 10% of the unpaid balance.10Justia. Connecticut Code 12-735 – Failure to Pay Tax or Make Return Interest runs at 1% per month, or any fraction of a month, from the due date until the balance is paid.
After you file, track a refund through myconneCT under “Where’s My Refund?” Paper returns take 10 to 12 weeks to process during filing season and won’t appear in the system until processing finishes.11Connecticut State Department of Revenue Services. Check the Status of Your Income Tax Refund E-filed returns move considerably faster. Allow at least two business days after DRS processes a direct deposit for the funds to land.