How long do I have to make an R&D claim?

The time limit

For accounting periods beginning on or after 1 April 2023, an R&D claim may be made, amended or withdrawn up to the last day of:

• two years beginning with the last day of the period of account, where that period of account is not longer than eighteen months; or
• 42 months beginning with the first day of the period of account, where it is longer.

The limit runs from the period of account — the period the accounts are drawn up for — rather than the accounting period. For a company with ordinary twelve-month accounts they are the same thing. For a long first period after incorporation, or the year a company changes its year end, they are not, and the deadline follows the accounts.

That gap can be wide. An accounting period can never exceed twelve months, but a period of account can, so a company extending a 31 December year end to 31 March has one fifteen-month set of accounts covering two accounting periods, and files a company tax return for each. Both of those returns carry the same R&D claim deadline, two years from 31 March — which gives the earlier of the two periods fifteen months longer than the December date would suggest. The same distinction governs the notification deadline, where it matters a great deal more, and it is worked through in Do I have to tell HMRC before I claim R&D tax relief?.

Because the same window governs making, amending and withdrawing a claim, it is also the window in which a claim already filed can be increased, reduced or taken out altogether.

Do not file on the last day

The statute gives you the period of “two years beginning with the last day of the period of account”. A period that begins with a given day includes that day. So for accounts made up to 31 December 2024, the two-year period beginning with 31 December 2024 runs out on 30 December 2026 — a day earlier than almost everyone assumes.

HMRC’s own guidance describes the limit as two years from the end of the accounting period and, so far as we have seen, HMRC does not take the point. It has not been tested. The contrast with the claim notification rule is striking, though: there, Parliament wrote “six months beginning with the first day after that period of account” precisely to produce a clean six-months-later date, and it did not do the same here.

Vantage’s position is that no claim is filed on the second anniversary itself. The cost of being a week early is nothing. The cost of being one day late is the whole claim.

How far back can I claim?

Two accounting periods, in the ordinary case. A company with a 31 December year-end looking at the position in September 2026 can still claim for the year ended 31 December 2025 and the year ended 31 December 2024. The year ended 31 December 2023 closed on 31 December 2025.

There is no mechanism for going back further. An R&D claim has to be made in a company tax return, and the return can only be amended within the statutory window; once the window closes, the return is fixed. Overpayment relief is not a way round this, because it is expressly unavailable where the taxpayer could have obtained the relief by making a claim in time and did not.

A first-time claimant should also check the claim notification position before assuming both years are available. The notification deadline for the earlier of the two years may already have passed even though the claim deadline has not, and where it has, that year is lost regardless.

The extension where HMRC removes a claim

There is one statutory extension. Where a company claimed enhanced relief or enhanced R&D intensive support, HMRC decided it was not entitled and removed the claim from the return, the company can instead claim the expenditure credit on the same expenditure up to whichever is the later of:

• 30 days after HMRC issues the notice amending the return; or
• where the point is appealed, 30 days after the appeal is finally determined.

It is a narrow provision and a short window, but it is the reason an unsuccessful intensive-support claim need not end with nothing.

Late claims

HMRC has discretion to admit a claim made after the deadline, and exercises it only in accordance with Statement of Practice 5 (2001). The test in that statement is whether the claim could not have been made in time for reasons outside the company’s control. Illness or unavoidable absence of the person who would have made the claim, at the critical time, with nobody else in a position to make it, is the kind of case it contemplates.

What it excludes is more useful to know:

• oversight or negligence by the company or its agent;
• failure, without good reason, to work out the figures in time;
• holding back to see how the claim would turn out; and
• illness or absence of the adviser rather than of the company.

“Our accountant did not tell us” is squarely within the excluded list. Applications must be made as soon as possible, and delay in applying is itself a ground for refusal.

Position for accounting periods beginning before 1 April 2023

The claim had to be made by the first anniversary of the filing date for the company tax return. For a twelve-month period of account the filing date is twelve months after the end of the period, so the deadline came out at two years after the period end — the same answer as the current rule, reached by a different route. The same HMRC discretion to admit late claims applied.

Those periods carry no claim notification requirement, but a claim for one of them made on or after 8 August 2023 does need an additional information form like any other.