R&D claim deadlines: what to diarise.

For a period of account of up to 18 months, the time limit is two years from the last day of the period of account. For a longer period, it is 42 months from the first day. The limit is set by paragraph 83E of Schedule 18 to the Finance Act 1998. An HMRC officer may allow a late claim, but you should never plan on that.

From the period of account, not from when the return was filed. A company that files its Company Tax Return nine months after year end still has the two years counted from the last day of the period. The filing date can matter for other reasons, such as the timing of the additional information form, but not for the claim time limit.

If the period of account is longer than 18 months, the limit is 42 months from its first day rather than two years from its last. For periods up to 18 months, it is two years from the end. Both the claim time limit and the notification window follow the period of account, so check each one using the same dates.

The legislation allows an HMRC officer to allow a late claim, but it is a discretion, not a right, and you should not rely on it. If you are close to or past the date, tell us at once. We can work out whether the claim is out of time, whether any discretion could be argued, and what to prepare.

For a 12-month period of account ending on 31 March 2025, two years from the last day gives 31 March 2027. By our arithmetic from the rule, a claim must reach HMRC by then. If the company is a first-time claimant, the claim notification deadline came earlier, six months after the period end, on 30 September 2025.

A 15-month period is under the 18-month limit, so the time limit is two years from the last day of the period. If the period ended on 31 December 2025, the claim deadline would be 31 December 2027, by our arithmetic. The notification deadline, if one applies, is six months after 31 December 2025, which is 30 June 2026.

They are separate and the notification comes first. A first-time claimant, or one who last claimed more than three years before the end of the notification period, must notify within six months of the end of the period. The claim itself has the two-year limit. Meeting the second does not rescue a missed first.

It has no separate calendar date. It must be submitted before, or on the same day as, the Company Tax Return containing the claim. So the practical deadline for the form is the date you file the return, and that date in turn must be within the claim time limit. We plan the work backwards from the deadline.

For a return filed on time, HMRC can normally open an enquiry within 12 months of the date it was filed. If the claim is made in a late or amended return, the window runs to the next quarter day after the first anniversary of filing. After that, HMRC can still raise a discovery assessment: normally 4 years after the period, 6 if careless, 20 if deliberate.

Yes, if the claim is still within its time limit. The old SME scheme or the old RDEC scheme applies to those periods, not the merged scheme. Old periods can also be relevant when correcting or amending earlier claims. The time limit is calculated in the same way from the period of account, so check the dates for each year.

A change can produce a short or long period of account, and the claim and notification deadlines follow the period of account that results. A period longer than 18 months has a different time-limit rule. If your year end has moved or is about to, send us the dates so we can recalculate before relying on the old pattern.

There is an extra 30-day window to claim the expenditure credit instead, after HMRC removes a claim for the additional deduction: an SME scheme claim for older periods, or an ERIS claim for periods from 1 April 2024. It is a narrow window and only applies in that situation. If HMRC has removed a claim and you want to preserve the option, tell us immediately and we will check the dates.

Yes. Under paragraph 83E, an R&D claim can be made, amended or withdrawn within the same time limit, normally two years from the end of the period of account. It is done by amending the Company Tax Return, and any additional information form must be up to date. Increasing a claim late in the window needs the same evidence as the original. If you think a past claim was too high, correction has its own route, so speak to us.

Well before the date. A claim needs technical interviews, cost mapping, a narrative, the additional information form and review, and a company that starts a month before the deadline has little room for error. We suggest starting at least three months ahead, or at the period end if you are a first-time claimant needing notification.

Use our claim time limit checker for the claim deadline and our claim notification checker for the notification position. Both run in your browser and store nothing. They give an indication based on the rules on this page, and we can confirm the exact dates for your company on a call.