There is no statutory format. HMRC does not prescribe a record-keeping system for R&D claims, so the question is not whether your records match a template but whether they evidence the two things a claim asserts: that the work met the definition of R&D, and that the costs claimed were incurred on it.
Estimates are allowed — but built, not asserted
HMRC does not require every figure to come from a contemporaneous record. Its guidelines for compliance say it is not unusual for R&D costs to be an estimated proportion of known expenditure, and ask that an estimate is arrived at using evidence and reason, with the amount shown to be based on facts. Where nothing was written down at the time, HMRC accepts that a detailed explanation provided later may be acceptable in some cases, and it expects the claim methodology, any sampling and the basis of any apportionment to be recorded. Reconstructing a year of engineering time from memory can therefore be a legitimate starting point when nobody was recording it.
Note what that is not. It is not a first-claim concession — HMRC publishes no such thing, and the latitude applies as much to a fifth claim as to a first. Nor is it permission to estimate loosely for ever: a company that has been claiming for years and still cannot say who spent what proportion of their year on which project is not relying on an HMRC allowance, it is relying on HMRC not asking. Our own position is simpler — from the point you know you are claiming, keep records as you go, so the estimate you defend in year three is tied to something recorded in year three.
What to keep once you are claiming
Five things do most of the work:
- timesheets or staff allocation records, showing who worked on which project and for what proportion of their time
- project documents describing the scientific or technological uncertainties, including what was not known and why existing knowledge was insufficient
- subcontractor and externally provided worker agreements, since the contractual position affects who can claim and under which cost head
- test results, including from the attempts that failed
- cost workings that tie to payroll and the ledger, with the apportionment basis written down at the time
None of this needs writing for HMRC. Design notes, technical decision records, stage-gate papers and internal write-ups all count; they simply need to exist. Our qualifying costs guide sets out what falls in each cost category and where the apportionments bite.
Timing matters more than format. Records made at the time the work was done are far more persuasive in an enquiry than reconstruction after the event, and the reason is straightforward: contemporaneous material was not written to win an argument, and it reads that way. A design note from eighteen months ago describing an approach that did not work carries weight no retrospective narrative can manufacture, however honest the narrative is. HMRC checked around one in six claims in 2023-24, its latest published figure, and our page on what HMRC will ask for in an R&D enquiry sets out the material a check typically requests, which is, in substance, the list above.
There is a commercial argument too, and it is not a small one. Good records make the next claim faster and cheaper to prepare. Much of the cost of preparing a claim is archaeology: working out who did what, when and why, from memory and half-remembered message threads. Companies that capture it as they go spend less time on their claim each year and end up with a stronger one.
Where to go next
Our HMRC enquiries guide explains what a check involves and how prepared claims hold up under one. If a project is starting now and you want to know what to capture before the work begins, that conversation is worth having at the outset rather than at the year end, and it costs nothing.
Written by Matthew Jones ACA CTA. Last reviewed July 2026.
Sources
- GfC3: Recommended approach to claims and record keeping (part 5) — HMRC on planning ahead, identifying a project retrospectively, the use of estimates and apportionments, and the evidence a compliance check may request.
- CIRD80550 and CIRD80560 — no R&D-specific record-keeping requirement, the general CTSA obligation, and the records HMRC expects to see.
- Check what R&D costs you can claim — the cost categories and the reasonable-share basis that apportionments have to meet.
This page describes the rules as they stood at the review date above, as general information rather than advice on your circumstances. For how that distinction works, see our terms; for an answer on your own facts, talk to us.