Do I have to tell HMRC before I claim R&D tax relief?

Who has to notify

For accounting periods beginning on or after 1 April 2023, a company cannot make an R&D claim once the claim notification period has ended, unless at least one of three things is true:

1. It made an R&D claim at some point in the three years ending with the last day of the claim notification period.
2. It filed a claim notification within the claim notification period.
3. The accounting period falls within the same period of account as another accounting period for which the company has already made an R&D claim or a claim notification.

Condition 1 is the exemption most companies rely on without knowing it exists. If you claim every year, you never notify. Condition 3 matters only where a period of account contains more than one accounting period.

Everyone else has to notify: first-time claimants, and returning claimants whose last claim falls outside the three-year window.

The three-year test is about the date you filed, not the years you claimed for

This is the point that catches people. The test asks whether an R&D claim was made — submitted to HMRC — during the three years ending on the last day of the claim notification period. It does not ask which accounting period that claim related to.

So a company that claimed for the year ended 31 December 2020, filing that claim in December 2022, looks at the filing date of December 2022 to determine whether it is exempt for a later period. The years covered by the claim are irrelevant to the test.

One further category is disregarded. If a claim for an accounting period beginning before 1 April 2023 got into the company’s tax return only because the return was amended on or after 1 April 2023, that claim does not count towards the exemption. The catch-up amended claim that a company files after realising it had been missing out is precisely the claim the rule ignores.

HMRC’s published guidance also states that a claim HMRC has rejected does not preserve the exemption. That is HMRC’s position rather than what the legislation says, and it is discussed below under where claims go wrong.

Working out your deadline

The claim notification period starts on the first day of the period of account and ends six months after the period of account ends.

Two things follow from that wording, and both are missed regularly.

It runs from the period of account, not the accounting period. For most companies these are the same twelve months and the distinction does not bite. When a company changes its year-end, the deadline moves with it. That case is worked through below.

You can notify at any point from the first day of the period. The window opens on day one of the period of account. Nothing stops a company from notifying in month two, and for a first-time claimant there is a good deal to be said for doing it immediately rather than carrying the deadline for eighteen months.

If you change your year end

An accounting period can never be longer than twelve months. A period of account can. That mismatch is where the arithmetic breaks.

Take a company with a 31 December year end that extends to 31 March. It draws up one set of accounts for the fifteen months from 1 January 2025 to 31 March 2026. That single period of account contains two accounting periods — the twelve months to 31 December 2025, and the three months to 31 March 2026 — and a separate company tax return is due for each. Two CT600s, one set of accounts.

But there is only one period of account, so there is only one claim notification period, and it covers both accounting periods. It runs from 1 January 2025 to 30 September 2026: six months after the fifteen-month accounts end, not six months after the December accounting period ends.

Two things follow, and they point in opposite directions.

• The deadline for the earlier accounting period is later than it looks. Counting from the December year end gives 30 June 2026. The real date is three months after that. A company being told in July 2026 that it has lost the year to 31 December 2025 may not have lost it at all — and that is worth checking before anyone writes the year off.
• The deadline moves when the year end does. It is fixed by the period the accounts are actually made up for, and that decision is often taken months later, by the accountant, for reasons that have nothing to do with R&D. A company that plans to extend and then does not is the dangerous version: the deadline snaps back from 30 September 2026 to 30 June 2026, and if that date has passed the year is gone.

Shortening a year end does the same thing in reverse and is the version that actually costs claims. Bring a 31 December year-end forward to 30 September, and the accounts cover nine months; the notification deadline is 31 March 2027, and anyone still working to the old December date is three months late.

The rest of what a year-end change does to a claim — two tax returns, two information forms, the cost split, and what a short accounting period does to the PAYE cap — is in What happens to my R&D claim if I change my year end?.

One point of relief in all this: because both accounting periods sit in the same period of account, a claim or a notification made for either one covers the other, under the third condition above. You do not need two notifications — though see below on why we file them anyway.

What the notification has to contain

The content is set by regulations, and the form asks for:

• the company’s registered name and unique taxpayer reference;
• the name, role, telephone number and email address of the officer of the company responsible for the claim;
• the details of any agent or adviser involved in the claim, including what they are acting on;
• the start and end dates of the accounting period, and of the period of account;
• the number of R&D projects; and
• a high-level summary of the planned R&D activities, showing how the work meets the statutory definition of R&D.

It is a short form. The summary of activities is a paragraph or two, not a technical narrative — that comes later, in the additional information form. But it must describe work that satisfies the definition, so someone who understands what the company is actually doing has to write it.

How to submit it

The notification is filed online through the Government Gateway by a company officer or an agent authorised to act for it. A third party who is not formally acting for the company cannot submit it.

You cannot get back into the form once it has been sent, so take a copy before you submit. When the tax return for the period is eventually filed, tick box 656 on the CT600 to confirm the notification was made.

If you miss the deadline

The claim for that accounting period is invalid. There is no appeal, and HMRC’s discretion to admit late R&D claims applies to the claim itself, not the notification, so it does not help here.

Three things are worth checking before accepting that outcome:

• Was there a claim inside the three years that everyone has forgotten? A claim filed by a previous adviser, in a year nobody has looked at, is enough.
• Is there another accounting period in the same period of account for which a claim or a notification has been made? If there is, condition 3 above may save the claim. This is the year-end-change case, and it is the one most often missed.
• Have the accounts been made up for a longer period than the accounting period? If the year-end moved, the real deadline may be months later than the one that was diarised.
• What about next year? Missing one year does not permanently disqualify the company, but it means there is now no claim within the three-year window, so the following period needs its own notification. This is where a single missed deadline turns into two lost years.

Position for accounting periods beginning before 1 April 2023

There was no claim notification requirement. Claims for those periods are made in the tax return in the ordinary way, subject to the time limits set out in How long do I have to make an R&D claim?. Those years are now closed for most companies, but they remain relevant for amendments and enquiries.