CT Quarterly Taxes: Due Dates, Payment Methods, and Penalties

If you earn Connecticut income without tax withheld, you owe Connecticut quarterly estimated taxes when your expected state income tax, after subtracting withholding and any Pass-Through Entity Tax Credit, is $1,000 or more for the year.¹ Payments go to the Department of Revenue Services in four installments, and missing them accrues interest at 1% per month on the shortfall.²

Who Has to Pay

Two things must both be true. Your Connecticut income tax for the year, minus withholding and any Pass-Through Entity Tax Credit, has to be at least $1,000. And your withholding alone has to fall short of your required annual payment, explained below.¹

The income that typically triggers the requirement is self-employment earnings from freelance work, consulting, sole proprietorships, partnerships, or LLCs. Rental income, capital gains, taxable interest and dividends, pension or annuity income without state withholding elected, gambling winnings, and unemployment compensation can also push you over the line.³

If employer withholding already covers what you owe, you don’t need to make estimated payments even with side income on top. And if you had zero Connecticut tax liability for the entire preceding year, and that year was a full 12 months as either a resident or a nonresident with Connecticut-source income, you owe nothing in estimated payments for the current year.³

How Much to Pay Each Quarter

Your “required annual payment” is the smaller of these two amounts:¹

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

The prior-year number is the safe harbor most people use because it’s a fixed, known amount. Pay 100% of last year’s tax across the four quarters and you won’t owe an underpayment penalty, even if this year’s income is much higher. Connecticut does not raise this to 110% for higher-income taxpayers the way federal rules do; it stays at 100% for everyone.¹

Divide the required annual payment by four. Each installment is 25%.¹ The worksheet in Form CT-1040ES walks through the math, accounting for projected income, credits, and withholding.⁴

Pass-Through Entity Tax Credit

If you’re a member of a partnership, S corporation, or LLC that pays Connecticut’s Pass-Through Entity Tax on your behalf, the credit you claim on your individual return counts toward withholding when you’re testing the $1,000 threshold and figuring whether withholding covers your required annual payment.¹ A sizable credit can reduce or eliminate the quarterly obligation entirely.

Adjusting If Your Income Shifts

Taxpayers with uneven income can use the annualized income installment method, which divides the year into separate computation periods and calculates each required payment based on income earned up to that point rather than assuming a flat 25% per quarter. Form CT-1040ES points to Worksheet CT-1040 AES and Informational Publication 2018(11) for that approach.⁴ If you overestimated or underestimated after the first installment, recalculate and adjust the remaining ones so the full year stays at or above 90% of actual liability.

Due Dates for 2026

The four installment deadlines for the 2026 tax year are:¹

April 15, 2026
June 15, 2026
September 15, 2026
January 15, 2027

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

You can skip the January 15 installment if you file your 2026 Connecticut return and pay the full balance by January 31, 2027. DRS will not charge underpayment interest on the fourth quarter when you meet that date.²

How to Submit a Payment

Online Through myconneCT

DRS’s online portal, myconneCT, replaced the older Taxpayer Service Center.⁵ You can pay by logging in to an account or as a guest. The guest option appears on the myconneCT homepage under the “Individuals” panel: select “Make a Bill Payment, Estimated Payment, or Return Payment.”⁶

Most people use Direct Payment, which pulls funds from a checking or savings account.⁷ Credit and debit cards work too, with a convenience fee shown before you confirm.⁶ You get a confirmation number immediately, and DRS applies the payment to the correct tax period. No printed voucher needed.

By Mail With Form CT-1040ES

To pay by check, complete the voucher from Form CT-1040ES, which tells DRS which tax period and account the payment belongs to. Make the check payable to “Commissioner of Revenue Services” and mail the voucher and check to:⁴

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

Sending a check without the voucher significantly delays processing. If you’re mailing close to a deadline, certified mail or a tracking service gives you proof of a timely postmark.

What Happens If You Underpay

DRS charges interest at 1% per month, or any fraction of a month, on each underpaid installment. The interest runs 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 set by statute and doesn’t move with federal rates.

The calculation runs quarter by quarter, not just on the yearly total. You can owe interest on one quarter even if your full-year payments ended up close to adequate. A short April installment keeps accruing interest through the following April unless you make it up.

To avoid the penalty, your combined withholding, estimated payments, and PE Tax Credit need to equal at least the smaller of 90% of this year’s tax or 100% of last year’s tax, and those amounts have to arrive on time each quarter.¹

One useful fix if you fall behind mid-year: increase your W-2 withholding for the rest of the year by filing a new Form CT-W4 with your employer. Withholding counts as paid evenly throughout the year regardless of when it actually comes out of your paycheck, so a boost in the fourth quarter can retroactively cover an earlier short quarter. Estimated payments only count for the quarter you make them.

When the Penalty Doesn’t Apply

No penalty applies if your tax, after withholding, comes to less than $1,000 on the return. And no penalty applies if you had no Connecticut tax liability at all for the prior year, provided that year covered a full 12 months.² Someone who moved to Connecticut in 2025 with no filing obligation that year wouldn’t owe a 2026 underpayment penalty even on a substantial first Connecticut return.

If you think DRS’s automatic calculation overstates what you owe, Form CT-2210 lets you compute the exact interest and claim applicable exceptions. The form also includes an annualized income installment option that can lower or eliminate interest on specific quarters by showing when the income was actually earned.⁸ Filing CT-2210 with your return is optional but worth it when the standard calculation isn’t in your favor.

Farmers and Fishermen

If at least two-thirds of your gross income comes from farming or fishing, the four-installment schedule doesn’t apply to you. You make one payment by January 15 of the following year. The required amount is the smaller of 66⅔% of the current year’s tax or 100% of the prior year’s tax (if the prior year covered 12 months and a return was filed). You can skip that January 15 payment and avoid the penalty entirely by filing your Connecticut return and paying the full balance by March 1.²

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