Where the worry comes from
Two separate fears sit underneath this question, and only one is true
They're worth pulling apart. One is that HMRC won't take a small claim seriously. The other is that no adviser will want to prepare it. Only one of those is actually true.
HMRC doesn't grade claims by size
There's no minimum claim value in the rules
Nothing in HMRC's published guidance treats a small claim as inherently less credible than a large one. Compliance checks look at the quality of the evidence behind a claim (how specific the technical narrative is, and whether the uncertainty and its resolution are actually described), not the pound figure attached to it. A thin, boilerplate narrative on a £200,000 claim draws exactly the same kind of scrutiny as one on a £15,000 claim. Size isn't the variable HMRC is checking.
The adviser market
A percentage fee makes the arithmetic work against small claims
Most R&D advisers price on a percentage of the claim's value, on a no-claim-no-fee contingency basis (see the fee comparison). That model works well on a large claim and badly on a small one: the time it takes to write a proper technical narrative and cost breakdown doesn't shrink much just because the claim is smaller, but the fee it generates does. A firm running a contingency book naturally gravitates towards the claims that make that arithmetic work, which tends to mean the larger ones.
HMRC's own statistics show the shape of this. In the R&D tax credits statistics for 2023 to 2024, 61% of all claims sit in cost bands up to £50,000, while 54% of the total value of relief claimed comes from claims of £1 million or more (see HMRC's R&D tax credits statistics, September 2025). That's a market where most of the volume is small and most of the money is concentrated at the top, which is exactly the shape that makes a percentage-fee model most attractive on the largest claims and least attractive on the smallest ones. It isn't proof that any specific small claim will be turned away, but it's consistent with what a percentage-fee adviser is actually incentivised to prioritise.
What this actually means for you: a meaningful share of genuine, valid claims are small enough that a percentage-fee adviser has limited commercial reason to take them on, or will only do so with a minimum fee that erodes much of the benefit. That's not a comment on whether the claim is real. It's a gap in who the market serves, and it's one of the clearer situations where filing it yourself isn't a compromise. It's the option actually built for your size of claim.
What "small" doesn't excuse you from
The same narrative and evidence bar applies, whatever the claim's size
A small claim still needs the same things a large one does: a specific technical narrative, a genuine cost identification exercise, and an Additional Information Form submitted before or alongside the Company Tax Return (see what the form requires). None of that scales down with the claim value. What scales down is the amount of adviser time a fee can realistically buy, which is the actual constraint, not the legitimacy of the claim.
Decision helper
Alternatives and limitations
If size is the only reason you'd hesitate, see filing your own R&D claim for the full process, and evidence and records for what makes a claim of any size hold up. A handful of firms on our adviser register offer fixed rather than percentage fees. They're worth checking if you'd still rather have specialist input on a small claim.
