Connecticut taxes for startups and founders: R&D credits, the angel credit, QSBS, AMT and the New York commute

Connecticut adds its own layer to the founder tax decisions in our other guides. The state follows the federal QSBS exclusion and will pay cash for R&D credits a money-losing startup can't use. Three points need attention: a one-year break from federal R&E expensing on 2025 corporate returns, an AMT tied to the federal one, and New York's claim on equity earned while commuting.

Key numbers: corporation tax 7.5%, $250 minimum · R&D credits of 20% incremental and 6% for small businesses · credit exchange 65%, or 90% for biotech, up to $1.5M a year · new 6% R&D credit for partnerships and S corps from 2026 · angel credit 25%, up to $100,000 per investor per company · top income tax rate 6.99%.

How Connecticut taxes a startup C corporation

A C corporation doing business in Connecticut pays the greatest of 7.5% of its Connecticut net income, a capital base tax, or a $250 minimum. The 10% surtax, extended through 2028, applies only to companies with $100 million or more of federal total income or in a combined unitary group, and never to the minimum.

For a startup still losing money, two more rules matter:

• Net operating losses from income years beginning in 2025 or later carry forward 30 years, but can offset only 50% of income in a profitable year.
• The capital base tax is 0.16% of apportioned capital for 2026, 0.11% for 2027, and zero from 2028.

R&E deductions on 2025 Connecticut returns

Connecticut's corporation business tax disallowed §174A expensing for 2025 income years only. Under Public Act 26-68, corporations deduct research costs paid or incurred from 2022 through 2025 under §174 as it read on July 3, 2025, which means five-year amortization for domestic research. Connecticut follows §174A from 2026.

The act also disallows the deductions under §70302(f) of the 2025 federal law: the small-business retroactive election and the election to write off unamortized 2022–2024 costs in 2025 and 2026. For Connecticut, those costs appear to stay on the old schedule, though DRS hasn't issued guidance yet.

Penalty relief remains available to calendar-year companies only through Monday, November 16, 2026. The law waives penalties and interest only on extra tax paid by the later of November 15, 2026 or the return's original due date, ignoring extensions. November 15 fell on a Sunday, and Connecticut's weekend rule (CGS §12-39a) treats a payment on the next business day as timely, though DRS hasn't addressed this deadline specifically. A fiscal-year company whose return for an income year beginning in 2025 is due later has until that due date.

The personal income tax wasn't changed, so S corporation and partnership owners appear to follow the federal deduction.

The R&D credits a startup can claim

C corporations can claim two credits on research done in Connecticut, and a small company with no tax liability can exchange both for cash. Partnerships and S corporations have a new credit from 2026.

Spending that earns the 20% credit is subtracted before figuring the 6% credit, so no dollar counts twice.

The credit exchange is open to a company with prior-year gross income of $70 million or less that can't use its credits because it has no corporation tax liability. Such a company can exchange the current year's credits for a refund of 65% of their value, or 90% for a small biotechnology company. Paying only the $250 minimum, or the capital base tax in a year with no net income, doesn't count as a liability. Refunds are capped at $1.5 million per income year.

Three rules trip companies up:

• The application, Form CT-1120 XCH, must be filed with a timely return, including extensions, and never later.
• Only credits earned in the current year qualify. Credits carried forward from earlier years can't be exchanged.
• The 6% credit is a "rolling" credit, meaning only one-third of a year's amount is allowed that year, so only that third can be exchanged. The rest carries forward for up to 15 years.

For the new pass-through credit, the business applies to the Department of Economic and Community Development (DECD) to reserve credits, verifies its actual spending within 90 days after year-end, and receives a voucher. Reservations are capped at $1.5 million per business and $25 million statewide each year. Owners claim the credit before other credits, and any excess over an owner's Connecticut income tax can be exchanged for 65%, or 90% for biotech, with the return.

Worked example: a Stamford software startup

A hypothetical seed-stage software company in Stamford is a Delaware C corporation with all its engineers in Connecticut. Its 2025 gross income was $900,000, and it has a tax loss for 2026, so it owes only the minimum or capital base tax.

• Connecticut research spending: $1,500,000 in 2026 and $1,100,000 in 2025.
• 20% credit: 20% × the $400,000 increase = $80,000.
• 6% credit: 6% × ($1,500,000 − $400,000) = $66,000, of which one-third, $22,000, is allowed for 2026.
• Exchange: 65% × ($80,000 + $22,000) = $66,300 in cash, requested on Form CT-1120 XCH with its 2026 return.
• The remaining $44,000 of the 6% credit carries forward against future Connecticut tax.

A small biotech company with the same numbers would get 90% × $102,000 = $91,800. As an S corporation with a DECD reservation, the company would instead earn 6% of the full $1,500,000, or $90,000, used first against its owners' Connecticut income tax, with any excess exchangeable at 65%. The same wages may also earn the federal credit and payroll tax offset, covered in our §174A and R&D credit guide.

The Angel Investor Tax Credit

New reservations are not available until July 1, 2027. The credit equals 25% of an accredited investor's cash investment of at least $25,000 in a business approved by Connecticut Innovations (CI), but the fiscal 2027 allocation is fully reserved. CI says new credits and applications open July 1, 2027. The statute bars reservations for investments made on or after July 1, 2028, so fiscal 2028 is the last scheduled round.

• Caps: $500,000 of credits per investor for life. CI's July 2026 guidelines limit eligible investment to $400,000 per company per investor or household, a $100,000 credit. The program is capped at $5 million of credits a year.
• Timing: the investor needs a reservation before investing, and it expires after 90 days. The credit is claimed for the year of the investment, carries forward five years, and can be sold or transferred.
• Company requirements: the company must have its principal place of business in Connecticut, under $1 million of gross revenue in its latest year, fewer than 25 employees, under seven years of operating in Connecticut, and under $2 million of credit-eligible investment, and it must be primarily owned by its management. At least 50% of its employees must be Connecticut residents, down from 75% on July 1, 2026.
• Who can't claim it: venture capital companies, banks, and anyone controlling 50% or more of the company, so a controlling founder can't claim it on their own company.

QSBS gain in Connecticut

Connecticut imposes no tax on QSBS gain that is excluded federally. Its income tax starts with federal adjusted gross income, and its list of add-backs has nothing for gain excluded under §1202, so excluded gain never enters Connecticut income. We're highly confident in this reading of the statute, though DRS hasn't published guidance specific to QSBS.

Gain that isn't excluded, such as half the gain on a three-year sale of stock issued after July 4, 2025, is taxed at Connecticut's regular rates of up to 6.99%, and the state has no lower capital gains rate. If you give shares to trusts to multiply the exclusion, Connecticut's own gift tax filing rules apply, as our QSBS guide explains.

Connecticut's AMT on ISO exercises

Connecticut does have an AMT, but it applies only if you owe federal AMT. The Connecticut minimum tax is the lesser of 19% of your federal tentative minimum tax or 5.5% of your federal alternative minimum taxable income, and you pay the excess over your regular Connecticut tax on Form CT-6251. Any Connecticut AMT you pay can come back as a credit in later years on Form CT-8801.

Because 19% of federal tentative minimum tax is often below your regular Connecticut tax, a measured ISO exercise can trigger federal AMT but no Connecticut AMT, while one large exercise can trigger both. Our ISO and AMT guide shows an example.

Founder equity and the New York commute

Connecticut taxes residents on all their income, including salary, option spreads, restricted stock and RSU income, and gains on sale, at rates up to 6.99%. If you live in Fairfield County and work in New York City, or did when you received equity, New York taxes the income from work done there, and Connecticut gives a credit for that tax.

• New York sources stock option and restricted stock income by your New York workdays between grant and vesting (Form IT-203-F), even after you leave the job. If your primary office is in New York, normal workdays at home count as New York days unless your home office is a bona fide employer office.
• Investment gains are treated differently, because New York generally doesn't tax a nonresident's gain on selling stock. A Connecticut founder's exit gain is therefore taxed by Connecticut, and excluded there too if it qualifies as QSBS.
• An 83(b) election also helps, because restricted stock covered by an 83(b) is taxed at grant, usually near zero, which leaves New York little to allocate later.
• Connecticut's credit can't exceed the Connecticut tax on that income, so you effectively pay the higher of the two states' taxes. New York City's income tax doesn't apply to nonresidents.
• A Stamford company's New York-resident employees owe Connecticut tax on Connecticut workdays once they spend more than 15 days a year in the state. Because New York has a convenience rule, they also owe it on days they work from home for their own convenience.

Common mistakes

1. Filing Form CT-1120 XCH after the return's due date, or trying to exchange credits carried forward from earlier years.
2. Assuming the full 6% credit can be exchanged in the year it's earned, when only the one-third allowed that year can be.
3. Carrying the federal §174A deduction onto a 2025 Form CT-1120.
4. Investing before getting an angel credit reservation.
5. Not keeping workday records for equity granted while you worked in New York.

How Summer Associates helps

Summer Associates, based in Stamford, runs R&D credit studies that cover the Connecticut credits and the exchange application, models ISO exercises against federal and Connecticut AMT, and reviews how New York sources equity income for founders who commute.

This guide is general education based on federal and Connecticut law as of 2026-11-15. State rules differ and facts matter. Before acting, get advice for your situation from Summer Associates or another qualified advisor.