What Is Form CT-1040NR/PY and Who Needs to File?

Form CT-1040NR/PY is Connecticut’s income tax return for nonresidents and part-year residents. You file it to report income connected to Connecticut and to calculate the tax the state is owed on that income. The form applies Connecticut’s regular tax rates to your entire federal adjusted gross income as if you were a resident, then scales the resulting tax down to the share of income that actually came from Connecticut sources.

Who Has to File

Connecticut sorts individual taxpayers into three groups. Full-year residents file Form CT-1040. Everyone else uses CT-1040NR/PY. A part-year resident is someone who moved into or out of Connecticut during the year and changed their permanent legal home in the process. A nonresident is someone whose permanent home sat outside Connecticut for the full year.

You need to file CT-1040NR/PY if any of the following is true:

Connecticut income tax was withheld from your pay.
You made estimated tax payments to Connecticut.
Your gross income from all sources meets the threshold for your filing status: $15,000 single, $24,000 married filing jointly or qualifying surviving spouse, $19,000 head of household, or $12,000 married filing separately.

Even if your income falls below the threshold, file a return when Connecticut tax was withheld so you can claim a refund.¹

A narrow exception lets some people domiciled in Connecticut be treated as nonresidents. You qualify only if, for the entire tax year, you kept no permanent place of abode in Connecticut, kept a permanent place of abode outside the state, and spent 30 days or fewer inside Connecticut. Fail any one of those tests and the state treats you as a resident.²

What Counts as Connecticut-Source Income

Connecticut-source income (CSI) is the figure the whole return turns on. For nonresidents, it includes:

Wages, salaries, fees, and commissions for work performed inside Connecticut.
Rental income from Connecticut real estate and gains from selling it.
Your share of income from a business, trade, or profession carried on in the state, including distributive shares from a partnership or S corporation operating there.
Lottery and casino winnings from Connecticut sources that generated a federal Form W-2G.
Payments under a covenant not to compete tied to Connecticut.

Several categories that appear on your federal return are excluded. Interest, dividends, and capital gains from stocks, bonds, and other intangibles are not CSI unless the property is used in a Connecticut business. Distributions from qualified retirement plans and pensions are generally excluded for nonresidents.

Remote Work and the Convenience of the Employer Rule

If you live outside Connecticut and work remotely for a Connecticut employer, the state applies a reciprocal convenience of the employer rule. It only activates if your home state imposes a similar rule. The clearest case is New York residents working for Connecticut employers.³

When the rule applies, days you worked from home across state lines may still be sourced to Connecticut unless your remote arrangement exists because the employer requires it rather than because you prefer it. You carry the burden of proving employer necessity, and the standard is demanding. If your home state does not impose a convenience rule, Connecticut generally will not either, and only days you were physically present in the state count toward CSI.

The Working-Days Allocation

When you work for a single employer both inside and outside Connecticut, you allocate wages with a working-days fraction. The numerator is your Connecticut working days. The denominator is your total working days everywhere.⁴

Total working days means days you were expected to work. Weekends, holidays, vacation, and sick time do not count. Any day you spent partly in Connecticut and partly outside counts as a full Connecticut day. Days spent in Connecticut on ancillary activities (tasks secondary to your main duties that you normally perform elsewhere) can be excluded from the Connecticut count. You report the allocation to your employer on Form CT-W4NA so withholding tracks reality, and the wages you later report on Schedule CT-SI should reflect the same fraction.

How the Tax Is Calculated

The calculation runs in two steps.

First, calculate Connecticut tax on your entire federal AGI as if all of it were taxable in the state. You use the same brackets residents use. Connecticut has seven marginal rates:

2% on the first $10,000 (single) / $20,000 (joint)
4.5% on income from $10,001 to $50,000 (single) / $20,001 to $100,000 (joint)
5.5% on income from $50,001 to $100,000 (single) / $100,001 to $200,000 (joint)
6% on income from $100,001 to $200,000 (single) / $200,001 to $400,000 (joint)
6.5% on income from $200,001 to $250,000 (single) / $400,001 to $500,000 (joint)
6.9% on income from $250,001 to $500,000 (single) / $500,001 to $1,000,000 (joint)
6.99% on income above $500,000 (single) / above $1,000,000 (joint)

Head of household brackets differ.⁵

Second, multiply that hypothetical tax by the apportionment fraction. The numerator is your Connecticut AGI from Schedule CT-SI. The denominator is your federal AGI. If Connecticut AGI is $45,000 and federal AGI is $120,000, the fraction is 37.5%, and you owe 37.5% of the step-one tax.

Schedule CT-SI and CT-1040AW

Schedule CT-SI builds the numerator. You list each income, gain, loss, and deduction item from your federal return, but only to the extent each is derived from Connecticut sources. Part 1 covers income items; Part 2 covers adjustments directly related to that income.⁶

Part-year residents complete Schedule CT-1040AW first. It splits your income between your resident period, when everything you earned anywhere counts, and your nonresident period, when only Connecticut-sourced income counts. The combined totals then feed Schedule CT-SI.⁷

Modifications and Prorated Deductions

Connecticut does not accept your federal AGI as-is. Schedule 1 of the form lists state-specific additions and subtractions that flow into Schedule CT-SI.

The most common addition is interest from municipal bonds issued by states other than Connecticut, which is federally exempt but added back here. The most valuable subtraction for many filers is the pension and annuity income deduction. You can subtract 100% of federally taxable pension income if your federal AGI is below $75,000 single or $100,000 joint, with the subtraction phasing out to zero as AGI reaches $100,000 single or $150,000 joint.⁸ For nonresidents this subtraction rarely matters because pension distributions are already excluded from CSI. Part-year residents can benefit for pension income received during their Connecticut months.

For nonresidents, modifications must relate to Connecticut-sourced income. You do not add back out-of-state municipal bond interest unless the bonds are held in a Connecticut business you operate. Members of pass-through entities receive a Schedule CT K-1 showing the specific modifications to include.⁹

Your standard deduction and personal exemptions are prorated using the same apportionment fraction. If Connecticut income is 40% of your federal AGI, you claim 40% of the deduction amount for your filing status. Nonresidents and part-year residents cannot itemize on this form.

Credits

One point catches many filers: nonresidents cannot claim the credit for income taxes paid to other states on the Connecticut return. That credit is for part-year residents only.¹ A nonresident facing tax on the same income in their home state generally claims relief on the home state’s return instead.

Part-year residents who paid tax to another state on income Connecticut also taxed can claim the credit to avoid double taxation. Attach a copy of the other state’s return. The credit is capped at the lesser of the tax actually paid elsewhere or the Connecticut tax attributable to the double-taxed income.

Other credits, including the property tax credit and the earned income tax credit, may also be prorated by the ratio of Connecticut AGI to federal AGI. Check each credit’s instructions for how proration applies.

Estimated Tax Payments

You must make quarterly estimated payments if you expect your Connecticut tax after withholding and any pass-through entity tax credits to be $1,000 or more.¹⁰ This frequently catches nonresidents with business or rental income that is not subject to Connecticut withholding at the source.

For the 2026 tax year, installments are due April 15, June 15, and September 15 of 2026, and January 15, 2027. Each payment should equal 25% of your required annual payment.¹¹ Your required annual payment is the lesser of 90% of the tax shown on your current year return, or 100% of the tax on the prior year return if it covered a full 12 months. If you had no Connecticut tax liability for the prior year, no estimated payments are required for the current year.

Underpayment interest runs at 1% per month on any shortfall, from each installment’s due date until the earlier of the return due date or the date you pay.

Deadlines, Extensions, and Penalties

Form CT-1040NR/PY for tax year 2025 is due April 15, 2026. When the date falls on a weekend or legal holiday, it moves to the next business day.¹² The Department of Revenue Services recommends electronic filing through the myconneCT portal, which handles returns, extensions, estimated payments, and refund tracking.¹³ Paper filers mail the completed return and schedules to the address in the instructions. Payments can be made through myconneCT by ACH debit or by check payable to the Commissioner of Revenue Services.

To buy time, file Form CT-1040 EXT before April 15 for a six-month extension to October 15.¹⁴ The extension covers filing only. You still have to estimate your liability and pay it by April 15.¹⁵

Missing the deadline triggers two penalties. Late filing is a flat $50. Late payment is 10% of the unpaid balance. On top of both, interest accrues at 1.25% per month on unpaid tax, with partial months counting as full months.¹⁶

Keep Your Records

Hold the filed return, every supporting schedule, your W-2s and 1099s, and your documentation of Connecticut working days for at least three years from the filing date or the original due date, whichever is later. The review window stretches to six years if you reported less than 75% of the income you should have, and there is no time limit if you never filed.¹⁷

For nonresidents who allocate wages with the working-days formula, the record of days spent in Connecticut matters most. Calendars, travel receipts, building access logs, and employer attendance records all serve as evidence if the Department of Revenue Services questions your allocation. Without that documentation, the default assumption is that all wages are Connecticut income, and reversing it after the fact is hard.

1
Connecticut State Department of Revenue Services. Form CT-1040NR/PY Instructions
2
Legal Information Institute. Connecticut Agencies Regulations 12-701(a)(1)-1 – Resident of This State
3
Connecticut General Assembly. Convenience of the Employer Rule
4
Department of Revenue Services. Connecticut Income Tax Withholding Requirements
5
Connecticut General Assembly. Connecticut Income Tax Rates and Brackets Since 1991
6
Department of Revenue Services. Form CT-1040NR/PY Instructions – Schedule CT-SI
7
Department of Revenue Services. Schedule CT-1040AW – Part-Year Resident Income Allocation
8
Connecticut General Assembly. Income Tax Exemptions for Retirement Income
9
Department of Revenue Services. Schedule CT K-1 – Members Share of Certain Connecticut Items
10
Justia Law. Connecticut General Statutes 12-722 – Underpayment and Overpayment of Estimated Tax
11
Connecticut State Department of Revenue Services. Connecticut Nonresident and Part-Year Resident Income Tax Information
12
Department of Revenue Services. DRS 2026 Tax Filing Due Dates Calendar
13
Connecticut State Department of Revenue Services. myconneCT
14
Legal Information Institute. Connecticut Agencies Regulations 12-723-1 – Extension of Time for Filing Returns
15
Connecticut State Department of Revenue Services. 2025 Income Tax Filing Season FAQ
16
Connecticut State Department of Revenue Services. Capital Gains, Dividends and Interest Income Tax
17
Internal Revenue Service. How Long Should I Keep Records