For accounting periods beginning on or after 1 April 2023, companies claiming R&D relief for the first time (or with no claim in the three years ending with the notification deadline — and claims made by amendment after 1 April 2023 for earlier periods do not count) must send HMRC a claim notification. The window opens on the first day of the period of account, so you can notify as soon as the period starts; the deadline is 6 months after the period of account ends. Miss it and the claim is invalid, even if the tax return amendment window is still open. Full guide here.
Claim notification is the trap that silently kills otherwise valid claims. If your deadline is near, speak to us this week, not this quarter.
The claim notification window
Applies to accounting periods beginning on or after 1 April 2023. The deadline holds even where the tax return amendment window is still open.
We have assumed a 12-month period of account — change this date if yours is different.
Leave blank if the company has never claimed, or you are not sure — the checker will assume notification is needed. The three-year exemption is measured to the notification deadline, not from today, so the exact date matters.
This checker is provided for illustration only. It applies the standard rules to the dates you enter, but real positions turn on details it cannot see: the statutory definition of the period of account, the three-year look-back and its exceptions (amendments made after 1 April 2023 for earlier periods do not count as prior claims, and nor does a claim HMRC rejected by removing it from the return), periods of account longer than 12 months and the more than one filing date they carry, and HMRC's limited easements. The amendment window shown is the standard one. Its output is not tax advice and must not be relied on for any decision, filing or deadline. We build and check these tools carefully, but they are provided as they are, without warranty that they are accurate, complete or current: the rules change, and the tool may itself be wrong. To the fullest extent permitted by law, we accept no liability for any error in it, or for any loss arising from its use or from reliance on its output. Our full website terms apply. Before acting — especially where a deadline looks close or passed — have the position confirmed by a competent chartered tax adviser. We will check it properly.
Rates and rules last reviewed 31 July 2026.
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