How far back can I claim R&D tax credits?

An R&D tax relief claim must be submitted within two years of the end of the accounting period in which the qualifying R&D expenditure was incurred. This means you can claim for eligible costs, provided they fall within the relevant accounting period and the R&D claim is made before the statutory deadline. 

This time frame exists because R&D tax credits are claimed through your Company Tax Return (CT600) as part of Corporation Tax relief. Companies normally have 12 months from the end of their accounting period to file their Corporation Tax return, followed by a further 12 months in which they can amend that return. In practice, this creates a maximum claim window of two years from the end of the accounting period. 

If you’re making your first R&D claim, or you haven’t claimed within the last three years, you also need to submit a Claim Notification Form (CNF) to HMRC before making your claim. This form makes HMRC aware of your intention of claiming R&D tax relief on your project. 

The CNF must usually be submitted within six months of the end of the relevant accounting period. Missing either the notification deadline, where it applies or the two-year claim deadline could mean you’re no longer able to claim relief for that accounting period.