CT Quarterly Taxes: Who Owes, Due Dates, and Penalties

Connecticut quarterly taxes are the estimated income tax installments you send to the Department of Revenue Services when your paycheck withholding won’t cover what you’ll owe. You need to pay them if your Connecticut income tax for the year, minus withholding and any Pass-Through Entity Tax Credit, will be $1,000 or more.¹ Payments are due in four installments across the year, and missing one triggers interest at 1% per month on the shortfall.²

Who Owes Quarterly Payments

Two things have to be true. Your Connecticut tax for the year, after subtracting withholding and any Pass-Through Entity Tax Credit, must come out to at least $1,000. And your withholding alone must fall short of your required annual payment.¹

The income that typically pushes people over the line isn’t wages. It’s self-employment from freelance work, consulting, sole proprietorships, partnerships, or LLCs. Rental income, capital gains, taxable interest and dividends, pension or annuity income without state withholding, gambling winnings, and unemployment compensation all count too.³

One clean exemption: if you had zero Connecticut tax liability for the entire prior 12-month year and were a full-year resident or a nonresident with Connecticut-source income, you don’t owe estimated payments for the current year at all.³² That’s the practical first-year rule for people who just moved to Connecticut.

If wage withholding already covers your total Connecticut tax, no quarterly payments are needed, even with side income. Run the numbers early in the year so April doesn’t surprise you.

How Much to Pay

Your required annual payment is the smaller of two figures.¹

90% of your current-year Connecticut tax.
100% of your prior-year Connecticut tax, if that return covered a full 12 months.

The prior-year figure is the safe harbor most people rely on. Pay 100% of last year’s Connecticut tax across the four installments and you’re protected from penalty even if this year’s income spikes. Unlike the federal safe harbor, Connecticut does not raise the bar to 110% for higher-income taxpayers. It stays at 100% for everyone.¹

Once you have that required annual payment, split it into four equal installments of 25% each.¹ Form CT-1040ES contains a worksheet that walks through the calculation and accounts for your projected income, credits, and withholding.⁴

If you’re a member of a partnership, S corporation, or LLC that pays the Connecticut Pass-Through Entity Tax on your behalf, the resulting credit on your individual return counts toward your withholding when measuring both the $1,000 threshold and your required annual payment.¹ A sizable PE Tax Credit can shrink or eliminate your quarterly obligation.

Income doesn’t always arrive evenly. If yours doesn’t, recalculate each quarter. Overestimated? Cut the remaining installments. Windfall you didn’t expect? Raise them. Connecticut also permits an annualized income installment method for uneven earners, computed on Worksheet CT-1040 AES and explained in Informational Publication 2018(11).⁴

When Payments Are Due

For the 2026 tax year, the four deadlines are:¹

April 15, 2026 (first quarter)
June 15, 2026 (second quarter)
September 15, 2026 (third quarter)
January 15, 2027 (fourth quarter)

When a due date lands on a weekend or legal holiday, it rolls to the next business day. Electronic payments have to be submitted by 11:59 PM on the due date. For mailed checks, the postmark controls.

You can skip the fourth installment entirely if you file your 2026 Connecticut return and pay the full balance due by January 31, 2027. DRS won’t charge underpayment interest on the fourth quarter in that case.² Useful if your tax documents come together in January anyway.

How to Submit a Payment

Online Through myconneCT

DRS accepts estimated payments through its myconneCT portal, either from a logged-in account or as a guest.⁵⁶ Most people use Direct Payment, which pulls funds from a checking or savings account at no charge.⁷ Credit and debit cards also work, with a processor fee shown before you confirm. You get a confirmation number immediately, and DRS applies the payment to the correct quarter automatically. No voucher needed when you pay online.

By Mail With Form CT-1040ES

If you’re paying by check, use the payment voucher from Form CT-1040ES so DRS knows which period and account the money belongs to. Make the check out to “Commissioner of Revenue Services” and send the voucher and check to:⁴

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

A check without the voucher can sit in processing for a while. Close to a deadline, certified mail or a tracked service gives you postmark proof if a dispute comes up later.

Farmers and Fishermen

If at least two-thirds of your gross income comes from farming or fishing, the four-installment schedule doesn’t apply. You make a single estimated payment by January 15 of the following year. The required amount is the lesser of 66⅔% of the current year’s tax or 100% of the prior year’s tax on a 12-month return. You can also skip that installment entirely by filing your return and paying the full balance by March 1 of the following year.²

What Happens if You Underpay

Interest runs at 1% per month, or fraction of a month, on any underpaid installment. It accrues from the installment due date until the earlier of April 15 of the following year or the date you actually pay.² The rate is fixed by statute and doesn’t move with federal rates.

DRS calculates the interest quarter by quarter, not on your annual total. A short first-quarter payment can accrue interest for the full year even if your later installments were plenty. So you can meet the annual number and still owe penalty interest if the timing was off.

To stay clear of the penalty, make sure total payments (withholding + estimated payments + any PE Tax Credit) hit at least one of these:¹

90% of the current year’s Connecticut tax
100% of the prior year’s Connecticut tax (on a 12-month return)

Whichever is smaller is your target, and the money has to arrive on time each quarter, not just by year end.

One useful move if you notice mid-year that you’ve underpaid: increase your Connecticut wage withholding by filing a new Form CT-W4 with your employer. Withholding is treated as paid evenly across the year no matter when it hits, so a larger year-end withholding can retroactively fix earlier quarters. Estimated payments only count for the quarter in which they’re made.

When the Penalty Doesn’t Apply

No underpayment penalty applies if the tax on your return after subtracting withholding comes to less than $1,000. And there’s no penalty if you had no Connecticut income tax liability at all for the prior year and that prior year covered a full 12 months.²

If DRS’s automatic calculation looks too high, file Form CT-2210 with your return. It lets you compute the exact interest, claim exceptions, and use the annualized income installment method to align payments with when you actually earned the income, which can reduce or eliminate interest on specific quarters.⁸ The form is optional, but it’s worth the time when the standard calculation would overcharge you.

1
Connecticut State Department of Revenue Services. Tax Information – Section: Estimated Tax Payments for Tax Year 2026
2
Justia Law. Connecticut General Statutes Title 12 Chapter 229 Section 12-722
3
Connecticut State Department of Revenue Services. IP 92(5.3) Estimated Connecticut Income Taxes
4
CT.gov. 2026 Estimated Connecticut Income Tax Payment Coupon for Individuals Form CT-1040ES
5
Connecticut State Department of Revenue Services. myconneCT
6
Connecticut State Department of Revenue Services. Filing and Paying
7
CT.gov. Making an Estimated Payment (Individual, Logged In)
8
CT.gov. Form CT-2210 Underpayment of Estimated Income Tax by Individuals, Trusts, and Estates