Definition
The two-year claim window is the statutory deadline for making or amending an R&D tax relief claim. A claim must be included in the company's corporation tax return or an amended return filed within two years of the end of the accounting period to which it relates. From 1 April 2023 the window was formally restated and must be read alongside the Claim Notification Form requirement for first-time and infrequent claimants. Missing the two-year deadline generally means the claim cannot be made at all.
How HMRC defines it
HMRC guidance on the claim deadline is at CIRD81800 of the CIRD Manual. The statutory basis is paragraph 83E of Schedule 18 to Finance Act 1998, which sets the two-year amendment window for CT returns. For claims requiring a Claim Notification Form, the separate six-month notification deadline applies in addition to the two-year filing deadline.
Practical example
A company with a 31 March 2023 year-end has until 31 March 2025 to file or amend its CT600 to include an R&D claim for that period. A claim submitted in April 2025 for that period is out of time and will be rejected, even if the underlying R&D activity and expenditure would otherwise qualify.