R&D tax credit claim deadlines

What is the deadline for making an R&D claim?

R&D tax relief is claimed through your Company Tax Return. HMRC sets the claim deadline by reference to your period of account (the period covered by your financial statements), not just a casual “two years after year end” rule.

HMRC’s current guidance states:

• If your period of account is 18 months or less, the deadline is 24 months from the last day of that period
• If your period of account is more than 18 months, the deadline is 42 months from the first day of that period.
  

This deadline applies to all accounting periods that fall within that period of account.  

How this works under the merged scheme and ERIS

For accounting periods beginning on or after 1 April 2024, most companies claim under the merged R&D tax relief scheme, with ERIS available for some R&D-intensive loss-making SMEs. These reforms change the mechanism and benefit rates, but they do not remove the need to meet HMRC’s claim time limits and process steps.  

The deadline is not the only date that matters

A lot of companies get caught out because the final claim deadline is not the only timing rule in play. Depending on your circumstances, you may also need to factor in:

Claim notification (advance notification)

If you are a first-time claimant or you have not claimed recently, you may need to submit a Claim Notification Form before you can make a valid claim for that period. The notification window runs from the first day of the period of account to six months after it ends.  

If you miss claim notification when it applies, the claim can be invalid even if you are still within the main CT600 amendment window.  

Additional information form (AIF)

For all claims, an AIF must be submitted before or alongside the Company Tax Return to support the claim. Treat this as part of your filing process, not an optional extra.  

Worked examples

Example 1: Standard 12 month year end

Your period of account is 1 January 2025 to 31 December 2025 (12 months).

Your claim deadline is 24 months from 31 December 2025, so 31 December 2027.  

If claim notification applies to you, your notification deadline would be six months after 31 December 2025, so 30 June 2026.  

Example 2: Long period of account (over 18 months)

Your accounts cover 1 January 2025 to 30 June 2026 (18 months plus).

Your claim deadline is 42 months from 1 January 2025.  

This is exactly why “it’s always two years after year end” is not safe as a universal rule.

Example 3: You discover qualifying R&D after filing the return

If you already filed your CT600 and later realise you should have claimed, you usually claim by amending the return, as long as you are within the time limit set out above. The key point is that the statutory deadline still applies.  

Can you extend your claim window by changing your year end?

Changing your accounting date can change your periods of account and therefore the deadline calculation but it is not a reliable “deadline hack”. It can also create knock-on effects, including shortening the claim notification window (because the notification deadline is tied to the period of account end date).  

If you are considering changing year end for commercial reasons, it is worth checking the R&D timing impact early, particularly where claim notification might apply.

What if you miss the deadline?

In general, if the statutory time limit has passed, the claim is out of time. HMRC can admit some late claims in limited circumstances, and their approach is set out in Statement of Practice 5 (2001). In plain terms, HMRC expects that the claim could not have been made within the time limit for reasons beyond the company’s control, and late acceptance is not the norm.  

If you think you are out of time, document the reason clearly and get specialist advice quickly. “We did not realise” is rarely enough on its own.