CT Estimated Taxes: Who Pays, Amounts, and Due Dates

If you expect to owe Connecticut $1,000 or more in income tax after withholding and credits, you have to prepay it in four quarterly installments rather than settling up once a year. Connecticut estimated taxes work on a pay-as-you-go basis for income the state isn’t already collecting through payroll withholding: self-employment earnings, investment gains, rental income, and anything else that reaches you without a W-2 behind it. Miss a quarter or pay too little, and the Department of Revenue Services charges 1% per month in interest on the shortfall.

Who Has to Pay

Two conditions have to be true before you owe estimated payments. Your Connecticut income tax for the year, after subtracting credits and any amounts withheld from wages or pensions, has to come to at least $1,000, and your withholding alone has to fall short of your required annual payment.¹

Freelancers, consultants, and sole proprietors are the usual candidates. With no employer pulling Connecticut tax out of each paycheck, the full job of staying current with the state falls on you. The requirement also catches W-2 earners who pick up meaningful income on the side: interest, dividends, capital gains, or rental profits. A single large stock sale or a strong year on a rental property can push you past the $1,000 line even when your paycheck withholding covers your salary.

Non-residents are in the same system. If you earn Connecticut-sourced income, such as business profits, professional fees, or rent from Connecticut property, you follow the same quarterly schedule as residents.

Connecticut taxes income on a graduated scale that runs from 2% to 6.99% across seven brackets, with the thresholds varying by filing status.² You’ll need a projected tax figure before you can tell whether you’re over the $1,000 threshold, so run your expected taxable income through the brackets for your filing status first.

How Much to Pay Each Quarter

Connecticut gives you two safe harbors. Hit either one and you owe no interest on underpayment, even if your final tax bill is higher than you projected.

The first option is to pay 90% of what you’ll actually owe for the current year.¹ This is a moving target because you’re estimating a year that hasn’t finished. It works when your income is steady and predictable.

The second option is to pay 100% of the tax shown on your prior-year Connecticut return, provided that return covered a full 12 months.¹ Most people lean on this method because the number is fixed from January: you know exactly what you owe for the whole year, and you divide it by four.

One catch for higher earners: if your Connecticut adjusted gross income was over $150,000 in the prior year, the prior-year safe harbor rises to 110% of last year’s tax.³ The 10% cushion keeps high-income filers whose earnings are climbing from leaning too heavily on a smaller prior-year figure.

Your required annual payment is the lesser of the two safe harbor numbers. Once you’ve picked that figure, each installment is 25% of it.⁴

If you belong to 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 personal liability and can shrink or wipe out what you owe in estimated payments. Form CT-1040ES won’t factor it in automatically, so adjust your worksheet by hand.

If Your Income Is Lumpy

Dividing your annual estimate into four equal pieces assumes you earn evenly through the year. For seasonal businesses or anyone sitting on an unpredictable capital gain, that assumption forces you to overpay early. The annualized income installment method lets you base each quarterly payment on income actually earned through that point in the year.

The trade-off is paperwork. You’ll track income month by month and recalculate before every deadline, following the worksheet in the Form CT-1040ES instructions. Any reduction you take in an early installment gets recaptured in a later one.⁴

Quarterly Due Dates

Connecticut’s deadlines line up with the federal schedule:¹

April 15 — first installment
June 15 — second installment
September 15 — third installment
January 15 of the following year — fourth installment

Each installment is 25% of your required annual payment. When a due date lands on a weekend or legal holiday, it rolls to the next business day. You can pay the entire year’s estimate with the April installment if you prefer to be done with it.¹

There’s a useful shortcut for the fourth installment. If you file your annual return and pay the full balance by January 31, Connecticut waives interest on the January 15 payment.¹

Farmers and fishermen follow a simpler calendar. You can make a single estimated payment covering the whole year by January 15, or skip estimated payments entirely by filing your annual return with full payment by March 1.³ The January 31 shortcut above does not apply to this group.

Fiscal-year filers pay on the 15th day of the 4th, 6th, 9th, and 13th months of their fiscal year.⁴

How to Pay

The DRS collects estimated payments through its myconneCT portal, and you don’t need an account to use it. On the Individuals panel, choose “Make a Bill Payment, Estimated Payment, or Return Payment.” ACH debit directly from a checking or savings account is free. Credit and debit cards work too but carry a convenience fee from the third-party processor. For ACH debit, you pick the withdrawal date when you set up the transfer, so you can schedule a payment early and have it hit on the due date.⁵

If you’d rather pay by mail, send a check or money order payable to the Commissioner of Revenue Services with the detachable voucher from Form CT-1040ES. The voucher carries your name, Social Security number, and the quarter it covers, which is how DRS credits the payment to the right period. Mail it to:⁶

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

Never send cash. For a large payment, certified mail or a traceable service gives you proof of timely delivery.

If you made estimated payments the prior year, DRS mails pre-printed coupons in mid-January. First-time filers can download Form CT-1040ES from the DRS website or skip paper entirely by paying through myconneCT.¹

What Happens If You Underpay

Connecticut doesn’t call it a penalty. It charges interest at 1% per month, or any fraction of a month, on the amount you underpaid.⁴ The label matters because the charge accrues automatically; there is no good-faith forgiveness. Interest runs from each installment’s due date until the earlier of April 15 of the following year or the date you actually pay.⁷

Each quarter stands on its own. You can owe interest on a missed first-quarter payment even if you overpaid later in the year. Payments get credited against unpaid installments in the order they came due, so catching up reduces interest but doesn’t erase what already accrued.⁴

Form CT-2210, filed with your annual return, walks through each quarter, compares what you paid against what was required, and calculates the interest on any shortfall. For this purpose, a “month” runs from the 16th of one month to the 15th of the next, and any partial month counts as a full one.⁷

Waivers are narrow. The most common ground is a casualty, disaster, or other unusual circumstance where you can show reasonable cause rather than willful neglect. You still have to file Form CT-2210 to request one. The annualized income installment method is the other way out: if your income was genuinely back-loaded, you can show that your payments matched what was actually earned through each due date and avoid interest on the earlier shortfalls.

If You Overpay

If your payments and withholding together come in higher than your actual tax, you have two choices when you file. Take the overpayment as a refund, or apply it to next year’s estimated tax. Applying it forward can shrink or eliminate the first installment you’d otherwise send in April.

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