CT Estimated Taxes: Who Pays, Quarterly Amounts & Due Dates

If you expect to owe $1,000 or more in Connecticut income tax after subtracting withholding and credits, you have to pay Connecticut estimated taxes in four quarterly installments during the year.¹ The installments are due April 15, June 15, September 15, and January 15 of the following year, and you avoid interest on any shortfall by paying at least 90% of the current year’s tax or 100% of last year’s tax (110% if your prior-year Connecticut adjusted gross income exceeded $150,000).

Who Has to Pay

The rule has two conditions and both must apply: your Connecticut tax liability for the year will be $1,000 or more after credits, and your withholding alone won’t cover your required annual payment.¹

The obvious group is anyone with self-employment income: freelancers, consultants, sole proprietors. No employer is pulling Connecticut tax from a paycheck, so the full quarterly burden is yours.

Investment and rental income catch a lot of people too. Interest, dividends, capital gains, and rental profits aren’t withheld on. One strong year for a rental property or a single sizable stock sale can push you past $1,000 even when your salary withholding looks fine on its own.

Non-residents earning Connecticut-source income follow the same schedule. If you run a business, provide professional services, or collect rent tied to Connecticut, you owe quarterly payments even if you live in another state.

How Much to Pay Each Quarter

Connecticut gives you two safe harbors. Meet either one and you owe no interest on underpayment, no matter how the year ends up.

90% of the Current Year

Pay at least 90% of the tax you’ll actually owe for the current year, spread across the four installments.¹ This is a projection, so it works best when your income is predictable. Connecticut applies a graduated rate structure from 2% to 6.99% across seven brackets that vary by filing status, and you’ll run your projected taxable income through those brackets to estimate the total.²

100% of Last Year’s Tax

Pay 100% of the total Connecticut income tax shown on your prior-year return, provided that return covered a full 12 months.¹ Most people prefer this one because the number is fixed from January.

Higher earners face a stricter version. If your Connecticut adjusted gross income exceeded $150,000 in the prior year, the safe harbor rises to 110% of last year’s tax.³

Your required annual payment is the lesser of the two safe harbor amounts. Divide it into four equal installments of 25% each.⁴

When Income Is Uneven

If your earnings come in bursts, such as a seasonal business or a one-time capital gain late in the year, the equal-installment approach can force you to overpay early. The annualized income installment method lets you base each quarterly payment on income actually earned through that point. It requires tracking income month by month and recalculating before each deadline, and any reduction you take early gets recaptured in a later installment. The worksheet accompanying Form CT-1040ES walks through the calculation.⁴

Pass-Through Entity Credits

If you’re a member of an S corporation, LLC, or partnership that pays the Connecticut pass-through entity tax, the entity’s payments generate a credit on your personal return. That credit reduces your individual liability and can reduce or eliminate your estimated tax obligation. Factor the expected credit into your worksheet; Form CT-1040ES doesn’t apply it automatically.

Quarterly Due Dates

The four Connecticut installment deadlines follow the federal calendar:¹

April 15 — 25% of your required annual payment
June 15 — 25% (50% cumulative)
September 15 — 25% (75% cumulative)
January 15 of the following year — 25% (100% cumulative)

When a due date falls on a Saturday, Sunday, or legal holiday, the deadline shifts to the next business day. You can also front-load and pay the full year’s estimate in April if you’d rather clear it.¹

One useful shortcut: if you file your annual Connecticut return and pay the full balance by January 31, Connecticut waives interest on the fourth installment.¹

Farmers and fishermen get a simplified schedule. You can make a single estimated payment for the full year by January 15, or skip estimated payments entirely and file your return with full payment by March 1.³

Fiscal-year filers use the same pattern as the federal system: the 15th day of the 4th, 6th, 9th, and 13th months of the fiscal year.⁴

How to Pay

DRS handles estimated payments through its myconneCT portal, and you don’t need an account to submit one. From the Individuals panel, choose “Make a Bill Payment, Estimated Payment, or Return Payment.” ACH debit from a checking or savings account is free; credit and debit cards work but carry a processor fee. With ACH debit you pick the withdrawal date when you set up the transfer, so you can schedule a payment weeks in advance and have it land on the due date.⁵

To pay by mail, use the detachable voucher from Form CT-1040ES with a check or money order payable to the Commissioner of Revenue Services. The voucher needs your name, Social Security number, and the quarter the payment covers; without it, DRS may not credit the right period. Mail to:⁶

Department of Revenue Services
PO Box 2932
Hartford, CT 06104-2932

Never send cash. For large payments, use certified mail or a traceable service to document the send date.

If you paid estimates last year, DRS mails pre-printed coupons around mid-January. First-time payers can download Form CT-1040ES from the DRS site or skip the paper entirely by paying through myconneCT.¹

What Underpayment Costs

Connecticut doesn’t call it a penalty. It charges interest at 1% per month, or fraction of a month, on any underpaid installment.⁴ Interest runs from each installment’s due date until you pay or until April 15 of the following year, whichever comes first.⁷

Interest is calculated separately for each quarter. Missing the April payment can cost you interest even if you overpay in June, because a later payment gets credited against the earliest unpaid installment first and reduces future interest without erasing what has already accrued.⁴

You calculate any interest owed on Form CT-2210 when you file your annual return. The form compares each quarter’s payment against what was required and applies the 1% monthly rate to any shortfall.⁷

DRS can waive interest for casualty, disaster, or other unusual circumstances where you show reasonable cause rather than willful neglect. You still file Form CT-2210 to request the waiver. The annualized income installment method is the other main way to avoid interest when income arrived late in the year: if your payments matched income actually earned through each due date, no interest applies to the earlier quarters.

If You Overpay

If your estimated payments and withholding come in higher than your final tax bill, you have two choices on your annual return. Take the excess as a refund, or apply it to next year’s estimated tax. Applying it forward can cover part or all of your April installment the following year.

1
Connecticut State Department of Revenue Services. IP 2005-28 Estimated Connecticut Income Taxes
2
Connecticut General Assembly. Connecticut Income Tax Rates and Brackets Since 1991
3
Connecticut State Department of Revenue Services. Connecticut Resident Income Tax Information
4
Connecticut General Assembly. Connecticut General Statutes Chapter 229 – Income Tax
5
Connecticut State Department of Revenue Services. Filing and Paying
6
Department of Revenue Services. 2026 Estimated Connecticut Income Tax Payment Coupon for Individuals
7
Connecticut Department of Revenue Services. Form CT-2210