How to Claim Connecticut Credit for Taxes Paid to Another State

Connecticut residents who paid income tax to another state on the same income Connecticut is taxing can claim a Connecticut credit for taxes paid to another state on Schedule 2 of Form CT-1040. The credit is the lower of two numbers: what you actually paid the other jurisdiction, or the share of your Connecticut tax that corresponds to that out-of-state income.¹ It covers other U.S. states, the District of Columbia, and political subdivisions like New York City. It does not cover foreign country taxes, and any credit that exceeds your Connecticut liability in a given year is lost rather than carried forward.

Who Can Claim the Credit

Three things all have to be true. You were a Connecticut resident or part-year resident during the tax year. You actually paid income tax to the other jurisdiction, not merely filed a return there. And the same income is taxed by both Connecticut and the other jurisdiction.¹ If Connecticut exempts the income, there is no dual taxation to solve, and no credit.

One point people miss: local income taxes count. New York City tax on wages you earned there qualifies, not just New York State tax.¹ What does not count: foreign country income taxes (those go on your federal return through the federal foreign tax credit), and non-income levies like sales tax or property tax paid to another state.

How Much the Credit Is Worth

Connecticut does not just subtract whatever you paid another state from your Connecticut bill. The credit is capped by a proportional formula.

For a full-year resident, the cap is: (Connecticut adjusted gross income from the other jurisdiction ÷ total Connecticut adjusted gross income) × total Connecticut tax.¹ You claim whichever is smaller, that cap or the tax you actually paid.

A quick example. Total Connecticut adjusted gross income of $200,000, $50,000 of which was earned in Massachusetts. Connecticut tax on the whole $200,000 comes to $10,000. The proportional cap is ($50,000 ÷ $200,000) × $10,000 = $2,500. If Massachusetts charged you $2,200, your credit is $2,200. If Massachusetts charged you $3,000, your credit is capped at $2,500 and you eat the difference.

There is also a floor. The credit cannot reduce your Connecticut tax below what you would owe if you simply left the out-of-state income off your Connecticut return entirely.¹ Because Connecticut uses graduated rates, dropping income can shift the remaining income into lower brackets, and the floor prevents the credit from producing a benefit that goes beyond neutralizing the double tax.

Earn income in more than one state? Calculate the credit separately for each jurisdiction, using the same proportional formula for each. You cannot pool your out-of-state taxes into one number.

How to Claim It on Your Return

You claim the credit by completing Schedule 2 of Form CT-1040, the Connecticut Resident Income Tax Return.² Fill out a separate Schedule 2 for each state or jurisdiction to which you paid tax.

Before you start, pull together:

The income tax return you filed with the other jurisdiction, showing income reported and tax calculated.
Proof you actually paid the tax, not just that it was assessed. A payment confirmation, bank record, or account transcript from the other state works.
W-2s or K-1s that show income allocated to the other state.

If you e-file through a preparer, the other state’s return does not have to be mailed to the Connecticut Department of Revenue Services, but the preparer has to keep the supporting documentation for four years from the filing date or due date, whichever is later.³ Keep your own copies at least that long.

Deadline, Extension, and Late Costs

The Connecticut deadline for the 2025 tax year is April 15, 2026.⁴ If your other state’s return is not finalized in time, you can request a six-month filing extension with Form CT-1040 EXT.⁵ The extension buys time to file, not time to pay. Estimate what you owe and pay by April 15.

Miss the deadline or underpay, and Connecticut charges a late payment penalty of 10% of the amount due, plus interest of 1% per month or fraction of a month until the balance clears.⁶ If you are waiting on a refund from the other state before filing in Connecticut, extend and pay your best estimate rather than file late.

Remote Workers With Out-of-State Employers

If you live in Connecticut and work remotely for a New York employer, New York may tax your wages under its “convenience of the employer” rule, which sources wages to the employer’s location rather than where you actually sit.⁷ Public Act 18-49 lets Connecticut residents claim the resident credit for taxes paid to another state under a convenience rule, so long as that other state applies a similar rule to its own nonresidents.⁸ New York qualifies, so Connecticut residents paying New York tax on remote-work wages can claim the credit.

The broader sourcing point matters too. Connecticut generally allows the credit only for taxes on income that Connecticut would consider taxable by the other state under its own sourcing rules.⁷ The convenience-rule reciprocal provision is the notable exception.

Part-Year Residents

Part-year residents use the same framework, but only for the period they were Connecticut residents. Only income earned in another state while you were a Connecticut resident counts, and the proportional cap uses your Connecticut adjusted gross income during the residency period rather than the full year.¹

If you moved to Connecticut mid-year and paid tax to your former state on income earned there before the move, that income usually is not eligible, because you were not a Connecticut resident when you earned it. Income earned in a third state during your Connecticut residency period would qualify. Timing matters more than geography.

Pass-Through Entity Members

If you are a member of a partnership or S corporation that paid an entity-level tax to another state under a regime substantially similar to Connecticut’s own pass-through entity tax, you can claim a credit against your Connecticut individual income tax for your share of that out-of-state entity tax. The calculation follows the same Section 12-704 rules as the standard credit.⁹

Pass-through returns can carry two separate credits at once: one for the Connecticut PTE tax the entity paid on your behalf, and another for entity-level taxes paid to other states. This is the point at which working with a tax professional generally pays off.

Mistakes That Cost People Money

The most expensive error is assuming the credit equals whatever you paid the other state. If the other state’s rate is higher than Connecticut’s, the proportional cap leaves you with a smaller credit than the check you wrote, and you will owe Connecticut the difference. Run the Schedule 2 math before setting estimated payments.

The second is claiming a credit on income Connecticut does not tax. No dual taxation means no credit, even if the other state taxed the income. Retirement and pension distributions cause a lot of this confusion because Connecticut treats them differently than many other states do.

The third is ignoring amendments. If you amend your other state’s return and your liability there changes, amend Connecticut and recalculate. Leaving the Connecticut return alone after an out-of-state amendment invites an audit adjustment and interest on the underpayment.

1
Justia. Connecticut Code 12-704 – Credits for Income Taxes Paid to Other States
2
Connecticut State Department of Revenue Services. Form CT-1040 Connecticut Resident Income Tax Return Instructions
3
Connecticut State Department of Revenue Services. Federal and State Electronic Filing for Preparers and Software Companies
4
Connecticut State Department of Revenue Services. Start of 2026 Tax Season
5
Connecticut State Department of Revenue Services. 2025 Income Tax Filing Season FAQs
6
Connecticut State Department of Revenue Services. Other Helpful Information
7
Connecticut General Assembly. Convenience of the Employer Rule (OLR Report 2025-R-0067)
8
Connecticut General Assembly. Public Act No. 18-49
9
Justia. Connecticut Code 12-699 – Pass-Through Entity Tax