Connecticut calendar and forms

Connecticut keeps its calendar locked to the federal one. Form CT-1040 is due the same day as Form 1040, April 15, 2027; the four estimated payments fall on the federal dates; and the extension runs six months to October 15, 2027. Two things are different. The extension is not automatic: it takes Form CT-1040 EXT by April 15, unless you filed a federal extension and expect no Connecticut tax due, in which case the federal one is enough. And the extension is to file, not to pay. Tax not paid by April 15 draws interest at 1% a month and a 10% penalty, extension or not.

The form side is longer than most people expect from a return that starts at federal AGI. There is one resident return, Form CT-1040, and its three built-in schedules: Schedule 1 for the additions and subtractions, Schedule 2 for the credit for tax paid to another state, Schedule 3 for the property tax credit. Then come the separate schedules that attach only when they apply: CT-EITC, CT-PE, CT-CHET, CT-Dependent, CT-1040WH. Most filers touch the return, Schedule 1 and Schedule 3. The rest of the list below is for people who moved, who work across the state line, who owe estimated tax, or who need to fix a return already filed.

The 2027 filing season, dated

How the extension really works

Form CT-1040 EXT, filed by April 15, gives six months to file. It does not give a day to pay. Anyone expecting a balance should send it with the extension, or pay it on myconneCT, by April 15; interest at 1% per month or part of a month and a late payment penalty of 10% of the tax due run from April 15 on whatever was not paid. A filer who requested a federal extension on Form 4868 and expects no Connecticut tax due does not need to file CT-1040 EXT; the federal extension covers the Connecticut filing date. A filer who owes should file the Connecticut form anyway, because it is also the payment voucher. Form CT-1127 is a separate application for more time to pay; it is not the same thing as the filing extension and is not granted as a matter of course.

Estimated payments

Connecticut requires estimated payments when the tax for the year, after Connecticut withholding and any pass-through entity tax credit, will be $1,000 or more and the withholding is less than the required annual payment. The required annual payment is the lesser of 90% of this year’s Connecticut tax or 100% of last year’s, if last year’s return covered twelve months; farmers and fishermen use 66⅔% in place of 90%. There is no 110% rule for higher earners. Interest on a late or short installment is 1% per month or part of a month, figured separately for each installment on Form CT-2210 and charged until the earlier of April 15 or the day the shortfall is paid. Payments go in on myconneCT or with the CT-1040ES coupon.

The people caught out are not usually wage earners. Pension and IRA payers withhold Connecticut tax only if asked on Form CT-W4P, and mandatory withholding on lump sums is suspended through 2027, so a retiree whose federal AGI crosses the $75,000 or $100,000 line and loses the pension subtraction often has no Connecticut withholding at all. The self-employed, owners of pass-through businesses that did not elect the entity tax, landlords, and anyone with a large capital gain or Roth conversion are the others.

The forms, in the order a filer meets them

Filing, paying and checking a refund

Most Connecticut returns are filed electronically with the federal return through tax software or a preparer, and the state refund arrives separately. The Department’s own system, myconneCT, files Form CT-1040 and CT-1040NR/PY free for anyone; it does not file the federal return, which must be filed separately with the IRS. Creating a myconneCT username takes the federal AGI from one of your last three Connecticut returns or a Connecticut driver’s license. The same site takes payments by bank debit with no fee, makes estimated and extension payments, shows payments already recorded, and lets you send a secure message to the Department. The IRS Direct File program, which Connecticut joined for the 2025 season, was not offered for the 2026 season, and the IRS has since ended the program.

Paper is slower and now riskier. The Department warns that the Postal Service postmarks mail when it is first processed, not when it is dropped in a box, and the postmark is what counts as the filing date under Connecticut law; a return mailed near the deadline should get a hand postmark at the counter. Paper returns take 10 to 12 weeks to process during the season and do not show in the refund system until processing is complete. Mailing addresses: with a payment, PO Box 2977, Hartford, CT 06104-2977; refund or no payment, PO Box 2976, Hartford, CT 06104-2976. There is a drop box for payments and documents at the street-level entrance of 450 Columbus Boulevard, Hartford, during business hours.

To check a refund, use “Where’s my Refund?” under the Individuals panel on myconneCT with your Social Security number, the tax year and the exact whole-dollar refund amount, or call the automated line, 800-382-9463 within Connecticut outside Greater Hartford or 860-297-5962 from anywhere, 24 hours a day. The phone system covers the current season only. For a person, the same numbers reach the Department Monday through Friday, 8:30 to 4:30; 860-297-4911 for TTY; DRS@ct.gov for general questions without attachments; and 860-297-5770 to schedule a video appointment. The eAssistant on the myconneCT home page answers routine questions around the clock.