The R&D claim notification deadline

Your claim notification deadline is the last day of the six months beginning with the day after your period of account ends: a period of account ending 31 December 2026 gives a deadline of 30 June 2027. The requirement applies to accounting periods beginning on or after 1 April 2023.

A company that has not made an R&D claim in the three years ending with its notification deadline, which includes any first-time claimant, must either notify HMRC by that deadline or make the claim itself by then. A claim made after the deadline without a notification is not valid, even where the deadline for amending the corporation tax return is still open. HMRC sets out the window and the three-year test in its guidance on telling HMRC you plan to claim. You may also see the requirement called pre-notification or advance notification. Whatever the name, it is the most unforgiving rule in the R&D regime: the notification is a short online form, but there is no way to make it late. To check your own date now, use our claim notification deadline checker.

Who must submit a claim notification?

For any accounting period beginning on or after 1 April 2023: any company that has not made an R&D claim in the three years ending with the notification deadline. That includes every first-time claimant. Such a company must either notify HMRC by the deadline or make the claim itself by then.

The requirement follows the accounting period, not the scheme. It applies to claims under the current schemes and to backdated claims for periods within its scope alike. If you are unsure which scheme your period falls under, start with which R&D scheme applies to your company.

Watch where the three years are measured to: the deadline, not the year end and not today. Because the deadline sits six months after the period of account ends, a past claim ages out of the test sooner than “the last three years” suggests. A company with a 31 December 2026 year end has a notification deadline of 30 June 2027, so only claims made on or after 1 July 2024 exempt it: a claim filed in March 2024 does not, however recent it feels. The shift helps at the other end — a claim made after the year end, during the notification window itself, counts.

Companies that have made a claim within that window are outside the requirement. There is one significant exception, covered below: a past claim made by amendment may not count.

Can the claim itself stand in for the notification?

Yes. The legislation bars only a claim made after the end of the claim notification period (CTA 2009 s1042C(2) for the merged scheme, s1045A and s1054A for ERIS and the old SME scheme, and the former s104AA for old RDEC). A claim HMRC receives by the deadline, in the return or an amended return, is not caught, whether or not the company has claimed before.

HMRC’s guidance treats first-time claimants differently. Under its heading for them it says: “You must submit the claim notification form within the claim notification period.” It offers the alternative of sending the claim itself by the deadline only to companies that have claimed before. The legislation draws no such line: a first-time claimant is simply a company with no claim in the three years. HMRC’s manual, at CIRD183000, sets the rule out in the legislation’s terms.

The route has a practical cost: the whole claim, with its Additional Information Form ahead of it, has to reach HMRC by the deadline, so the time it takes to prepare a claim has to fit inside the notification window. Notifying costs nothing and removes the question, so notifying is the safe course, and it is the one we take.

When is the claim notification deadline?

On the last day of the six months beginning with the day after the period of account ends. Not six months from the start of the period, and not from the date you file the return.

The window itself opens on the first day of the period of account, so a company that knows it will claim can notify well before the year end. The end of those six months is the deadline, not the point at which the window opens.

The period of account is the period for which you draw up accounts. For most companies it is identical to the corporation tax accounting period, but the two can diverge, for example where accounts cover more than twelve months. The six months always run from the end of the period of account, so where your dates diverge, confirm the correct end date before relying on a diary entry. Changing your year end moves that end date, and shortening it moves the deadline earlier — sometimes to a date that has already passed. What happens to an R&D claim if you change your accounting date works through the long and short periods a change creates.

Here is how the deadline falls for the four common year ends. The rule is the same every year; for any other year end, the notification checker works out the date.

A company with a 31 December 2025 year end had until 30 June 2026 to notify, or to make the claim itself. If it was in scope and did neither, no R&D claim can now be made for that year, however strong the underlying work.

Watch the exact day. The six months are counted from the day after the period of account ends, and the deadline is the last day of that six-month period. A 30 June year end therefore gives 31 December (the six months run 1 July to 31 December), while a 31 December year end gives 30 June. A diary entry that only records the month is how these get missed.

What happens if you miss the claim notification deadline?

If the company neither notified nor made the claim by the deadline, any claim it makes for that period afterwards is invalid, entirely. The amendment deadline for the tax return does not rescue it. A company can be comfortably within the two-year amendment window and still have no claim, because a claim made after the deadline needs a notification made in time, and a notification cannot be filed late. HMRC has no discretion to accept a late notification and there is no appeal route: where a notification was required and is missing, HMRC removes the R&D claim from the return as an error.

The rule bites hardest on start-ups. The earliest development years usually carry the heaviest qualifying spend and the deepest technical uncertainty, and they are precisely the years founders spend building rather than reading tax legislation. By the time R&D relief reaches the top of the list, the window on the most valuable period is often already shut. We set out how companies fall into the notification trap, and how to avoid it.

One consolation: the test is applied period by period. Missing the window for one accounting period does not poison later ones, so a company that has lost a year can still protect the next. The same rule also operates silently on backdated claims, where it has already extinguished claims for periods people assume are still open.

There is one narrow, closed exception. HMRC published guidance in autumn 2024 that it later corrected, and it operates an administrative easement for the companies caught in the interim: where the claim notification period ended between 8 September and 30 November 2024, and the company had made a valid claim for a pre-April 2023 period in an amendment submitted between 1 April 2023 and 30 November 2024, HMRC will allow the R&D claim despite the missing notification. If your deadline fell in that window, have the position checked before writing the period off — our deadline checker flags affected dates automatically.

Why might a past claim not protect you?

Because a claim that reaches a return only by an amendment made on or after 1 April 2023, for a period that began before that date, does not count as a prior claim for this test. A company whose only recent claim went in as, say, a 2024 amendment adding relief for its 2022 year end is treated as if it had not claimed at all. Until it has a claim that counts, it must notify, or make the claim itself, by each period’s deadline.

This wrinkle catches companies that consider themselves established claimants. If any of your recent claims went in by amendment rather than in an original return, check the position before assuming you are exempt.

What should you do now?

Act on whichever of these applies:

• Year end approaching or recently passed. Confirm whether you are in scope and diary the deadline immediately. The deadline checker gives you the date in seconds.
• Undecided about claiming. Our approach is to notify wherever a claim is realistically in prospect. Losing the option costs far more than the notification.
• Deadline already missed. Take advice before writing everything off. Other periods may still be open, and the next window can be protected.

Notification is the first of three procedural steps in every claim: the notification where required, the Additional Information Form with every claim, and the CT600 itself. Every other date in a claim — the filing date, the two-year claim window, the enquiry window and the discovery long-stops — is derived in R&D tax relief deadlines. Getting the procedure right matters because around one in six R&D claims was checked in 2023-24, HMRC’s latest published figure; our guide to HMRC R&D enquiries explains what that involves and how to respond.

Talk it through with a chartered adviser

Deadlines in this area do not move, and there is no late route once one has passed. LimestoneGrey is a firm of Chartered Tax Advisers and Chartered Accountants, regulated by ICAEW, specialising in R&D tax relief. Settling the notification question is part of how every engagement starts, so the option to claim is protected before anything else is discussed.

If your year end has passed, or is coming, and the notification question is unresolved, get in touch and we will settle it quickly. For the wider picture, start with our R&D tax relief guide.

Sources

• Tell HMRC you want to claim Research and Development (R&D) tax relief — the six-month notification window, the three-year test, the instruction to first-time claimants to submit the form, and the claim-by-the-deadline alternative it offers to companies that have claimed before.
• CTA 2009 s1042C, s1045A and s1054A — the restriction itself. No claim may be made after the end of the claim notification period unless the company claimed in the three years ending with its last day, notified within it, or claimed or notified for another accounting period in the same period of account. For old RDEC, s104AA was in the same terms.
• CTA 2009 s1142A — the claim notification period: from the first day of the period of account to the last day of the six months beginning with the day after it ends.
• SI 2023/813: claim notification & AIF regulations — the statutory content requirements for notification.
• CIRD183000 — the three-year test’s reference point, the amendment rule, and the autumn 2024 administrative easement.

CIRD183000 is indexed on our CIRD reference index, with HMRC’s own title for it, a line on what it says and the date HMRC last revised it.