R&D Binder

Short answer. An Illinois research credit you cannot use carries forward for 5 years, counted from the tax year you earned it, and it cannot be carried back. It offsets Illinois income tax only, not the personal property replacement tax. When you hold credits from several years, Schedule 1299 uses the ones closest to expiring first.

Key facts

Carryforward5 years from the year the credit was earned
CarrybackNone
What it offsetsIllinois income tax only (not the personal property replacement tax)
Order of useEarliest expiration first, then by credit code
Credit code5340 (the leading 5 marks a 5-year carryforward)
Authorized forTax years ending before Jan 1, 2037

How the five-year clock works

The clock starts in the year the credit is earned, whether or not you had tax to use it against.

The credit under 35 ILCS 5/201(k) is 6.5 percent of the amount your Illinois qualified research expenses exceed the average of the prior three years. It is nonrefundable, so in a year when your Illinois income tax is zero, the credit does nothing that year. The unused amount rolls forward for up to 5 years, measured from the year it was earned. There is no carryback to recover tax paid in an earlier year.

Illinois builds the carryforward length into its credit codes. The research credit is code 5340, and the leading 5 means a 5-year carryforward. The credit applies against Illinois income tax only. It does not reduce the personal property replacement tax, so a company that owes only that tax still banks the credit.

One filing rule catches pre-profit companies: Schedule 1299 must be filed in any year you earn a credit, even if it offsets no tax that year. Skipping the schedule in a zero-tax year is how a carryforward goes undocumented.

Which credits get used first

When several years of credit are on the books, Illinois decides the order for you.

Schedule 1299 applies credits by earliest expiration date first. Among credits that expire in the same year, it sorts by credit code. In practice this means your oldest research credit is always the next one consumed, which is the order you would pick anyway, since it is the first one at risk of lapsing.

The credit itself is authorized for tax years ending before January 1, 2037, under Public Act 104-468, signed in June 2026. Credit earned inside that window still follows the 5-year carryforward rule.

A nonrefundable credit

Illinois tax is what the credit waits for.

The credit is nonrefundable and offsets Illinois income tax only. A company that never owes Illinois income tax within the 5-year window loses the credit. That makes the timing of profitability the main planning question, more than the size of the credit.

An illustrative example

Round numbers for a hypothetical Illinois SaaS company, using only the rules above.

  1. Year 1. Illinois QRE is $1,000,000 against a prior three-year average of $600,000. The increase is $400,000, and 6.5 percent of that is a $26,000 credit. Illinois income tax is zero, so the full $26,000 carries forward. Schedule 1299 is still filed.
  2. Year 2. The company earns another $10,000 of credit and still owes no Illinois income tax. The balance is $36,000 across two vintages.
  3. Year 3. Illinois income tax is $8,000. The Year 1 credit expires first, so $8,000 comes from it, leaving $18,000 of Year 1 credit.
  4. Year 4. Tax is $12,000, all from Year 1 credit, which leaves $6,000.
  5. Year 5. Tax is $15,000. The last $6,000 of Year 1 credit goes first, then $9,000 of Year 2 credit. $1,000 of Year 2 credit remains, with time left before its own 5 years run out.

Why the records matter years later

A credit earned in one year may not be used until four or five years on.

The credit you finally use in Year 5 still rests on the research and wages from Year 1. If those records are thin when the credit is claimed against real tax, the carryforward is only as good as the file behind it. R&D Binder produces the federal Section 41 documentation the Illinois credit is built on, and your CPA files the Illinois return. Whether your facts qualify is your CPA's call.

The full state overview, the federal Section 41 work it builds on, and related state guides:

Sources

Every claim on this page traces to a primary authority. Each source below is independent and verifiable.

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