The R&D claim notification requirement

If your company is claiming R&D tax relief for the first time, or has not claimed in the previous three years, you must submit a claim notification to HMRC within six months of the end of your period of account. The rule applies to accounting periods beginning on or after 1 April 2023. Miss the window and the claim is invalid, even where the deadline for amending the tax return is still open.

You may also see this called pre-notification or advance notification. Whatever the name, it is the most unforgiving rule in the R&D regime: the notification itself 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?

Two groups of companies, for any accounting period beginning on or after 1 April 2023: those claiming R&D tax relief for the first time, and those that have not made an R&D claim in the previous three years.

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.

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

When is the claim notification deadline?

Six months from the end of the period of account. 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. Six months after the period ends 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.

Here is how the deadline falls for common year ends, and where each stood at the time of writing in July 2026.

A company with a 31 December 2025 year end had until 30 June 2026 to notify. If it was in scope and did not notify, no R&D claim can 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 window?

The claim for that period 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 valid notification is a precondition of claiming and 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.

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 amendments filed after 1 April 2023 that claim for earlier periods do not count as prior claims 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, and must notify for new periods.

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. Getting the procedure right matters because HMRC checks roughly one in six R&D claims; our guide to HMRC R&D enquiries explains what that involves and how we defend claims.

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 specialising in R&D tax relief regulated by ICAEW, and 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.

Written by Matthew Jones ACA CTA. Last reviewed July 2026.

Sources

• Tell HMRC you plan to claim — the six-month notification window and the three-year test.
• 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.