How far back can you claim R&D tax credits?

Do R&D tax credits expire?

Yes. A company has a deadline for each period it wants to claim for. HMRC's guidance sets it by reference to the period of account, which is the time covered by the company's financial statements. ^[1]

• For a period of account of 18 months or less, the deadline is 24 months from the last day of the period.
• For a period of account longer than 18 months, the deadline is 42 months from the first day of the period.

This is the deadline for all accounting periods that fall within that period of account. These rules sit alongside the two sets of schemes: accounting periods beginning before 1 April 2024 fall under the old RDEC and SME schemes, and later periods under the merged R&D scheme and enhanced R&D intensive support. ^[1]

For example, a company with a 12-month period of account ending on 31 December 2025 would have until 31 December 2027 under the first rule. ^[1]

Is there a shorter deadline for a first claim?

For accounting periods beginning on or after 1 April 2023, a company claiming for the first time must submit a claim notification form within the claim notification period. If it does not, the R&D claim will be invalid. ^[2]

The notification period starts on the first day of the period of account and ends 6 months after the period of account ends. HMRC gives an example where the period of account runs from 1 January 2024 to 31 December 2024, so the last date to notify is 30 June 2025. ^[2]

A company that has claimed within 3 years of the end of the notification period does not usually need to send the form again, with exceptions. These include a claim that HMRC rejected by removing it from the Company Tax Return. ^[2]

This means a company that has never notified HMRC may find that the notification window for an older period has already closed, even though the 24-month claim deadline has not. A specialist adviser can check which dates apply to each period, and our R&D tax relief services could help identify whether a claim for an earlier period may still be possible.

What else has to be in place before the claim?

An additional information form must be submitted before or on the same day as the Company Tax Return. If it is sent after the return, or not at all, the claim will not be accepted. ^[3]

Where a company has to notify again, for example because its last claim was more than 3 years before the end of the notification period, HMRC says it can either send the form or send the claim on the Company Tax Return or as an amendment, as long as the claim is received by the last date of the notification period. ^[2]

Can R&D credits be carried back?

HMRC's guidance does not describe the merged scheme credit as a carry-back claim. What its payment steps do allow is that, once the credit has been used against the current period's Corporation Tax, the remainder must be used to pay any outstanding Corporation Tax for other accounting periods. Amounts that are still unused can be carried forward. ^[1] The steps themselves are set out in our guide to calculating R&D tax credits.

How many years can HMRC go back?

This is a different question from the company's claim deadline. It concerns how long HMRC has to check a return or raise an assessment, and the limits are set by Schedule 18 of the Finance Act 1998. ^[4]

• HMRC may open an enquiry into a company tax return by giving notice within 12 months of the day the return was delivered, if it was delivered on or before the filing date. The rules differ for late returns, amended returns and some larger groups. ^[4]
• Outside an enquiry, an assessment generally cannot be made more than 4 years after the end of the accounting period. ^[5]
• Where a loss of tax is brought about carelessly, the limit is 6 years after the end of the accounting period. ^[5]
• Where it is brought about deliberately, the limit is 20 years. ^[5]

These limits apply across Corporation Tax. They are not specific to R&D, and the Act allows longer periods in some cases. If a business is worried about a period it filed some years ago, a qualified adviser can advise on the specific position.