The Connecticut R&D tax credit, explained
Connecticut runs two R&D credits, plus a cash exchange option for small businesses with no tax liability.
Last verified July 2026 against Connecticut Department of Revenue Services guidance.
The short answer
Connecticut has an active state R&D tax credit, actually two of them. One is a nonincremental credit based on total research spending. The other is a 20% incremental credit based on the increase in spending over a base period.
How the Connecticut credit works
For companies with gross income under $100 million, the nonincremental credit is a flat 6% of qualified Connecticut research spending. Larger companies use a sliding scale from 1% up to 6% depending on spending level. Neither version is directly refundable against Connecticut tax.
Qualified small businesses, meaning gross income under $70 million and no Connecticut corporation tax liability, can instead exchange unused credit for a cash refund: 65% of the credit value, or 90% for qualifying small biotechnology companies. That refund is capped at $1.5 million a year per company. Unused, unexchanged credit carries forward 15 years.
How it stacks with the federal credit
Connecticut's credit and the federal R&D credit both start from the same qualified research expenses, so one research study supports both claims.
Example: a Connecticut biotech startup with 10 scientists and an average salary of $112,000 spends $1,120,000 on qualified research. As a qualified small business, it claims the flat 6% nonincremental rate on the full amount, for a $67,200 Connecticut credit. With no state tax liability yet, it exchanges that credit for a cash refund at 65%, or about $43,680, higher still at 90% if it qualifies as a small biotech company. The same $1,120,000 in spending can generate a federal credit of roughly $67,000 to $112,000, and a company under $5 million in revenue can apply that federal credit against up to $500,000 of payroll taxes a year.
Because the Connecticut cash exchange gives real money to companies with no tax bill yet, it is worth checking every year, even for a company that expects to owe no Connecticut tax for several more years.
Takes about 60 seconds. No signup.
Eligibility and how to claim it
Any company doing qualified research in Connecticut can claim the nonincremental or incremental credit on its corporate tax return, with the rate depending on total gross income.
The cash exchange option is only for qualified small businesses: companies with gross income of $70 million or less in the prior year and no Connecticut corporation business tax liability for the current year. Qualifying small biotechnology companies get the enhanced 90% exchange rate.
Companies claim the nonincremental credit on Form CT-1120 RDC and the incremental credit on Form CT-1120RC. The cash exchange uses Form CT-1120 XCH. All are filed with the Connecticut Department of Revenue Services. Claimship prepares the underlying research study. The company's CPA decides which credit to claim, files the forms, and requests the exchange if eligible.
Official source: Connecticut Department of Revenue Services.
Carryforward and deadlines
There is no separate application window for the base credit. It is calculated and claimed directly on the Connecticut corporate tax return each year, with a 15 year carryforward for credits earned in income years beginning on or after January 1, 2021.
The cash exchange election is made on the same annual return. A company that wants the exchange should confirm its qualified small business status, including the gross income and no-tax-liability tests, before filing.