R&D tax credits for UK startups (2025 rules)

The 2025 landscape — what changed

For accounting periods starting on or after 1 April 2024, the two legacy schemes (SME + RDEC) merged into a single R&D Expenditure Credit (RDEC) scheme, paying 20% above-the-line. The previous SME scheme's headline rates (33%, then 27%, then 21.5%) are gone for most companies.

There's still a separate enhanced scheme for R&D-intensive SMEs: loss-making companies whose qualifying R&D is 30%+ of total expenditure pay a higher effective rate (~27%). Most early-stage tech startups qualify for this if they meet the ratio.

The merger was driven by HMRC's view that the SME scheme was being abused — by agencies promising claims with little substance, by claims for routine software work, and by "black box" claim factories. The new regime is tighter, more documented, and more frequently challenged.

What actually qualifies as R&D

HMRC's definition: an activity that seeks to achieve an advance in science or technology by resolving scientific or technological uncertainty. The advance must be in the field generally, not just in your business. Three tests:

1. Advance — your project aims to push the field forward, even incrementally. Building a better recommendation algorithm than what's in any public paper might qualify. Wiring together known APIs almost certainly doesn't.
2. Uncertainty — a competent professional in the field can't look at your problem and immediately know how to solve it. If the answer is googleable, it's not R&D.
3. Systematic investigation — you had hypotheses, tested them, learned from failures. You can describe what didn't work and why.

What HMRC has been rejecting

Common rejections in 2024-25 enquiries:

• SaaS feature work. "We built a checkout flow" isn't R&D, no matter how clever it felt. The technological uncertainty test fails.
• App development with mature stacks. React, Rails, AWS — putting these together doesn't resolve technical uncertainty.
• Routine integrations. Connecting Stripe to your CRM doesn't qualify, even if it took 3 months and was hard.
• Cosmetic / UX work. Even substantial design refresh doesn't qualify.
• Bookkeeping-as-R&D. Especially "our developer is the CTO and writes code, so 100% of his time is R&D".

What still qualifies (for tech startups)

• Novel ML/AI work — training a model on proprietary data with architectures not directly available off-the-shelf.
• Performance breakthroughs — getting a known algorithm to run 100x faster, with the technique not being public knowledge.
• Cross-platform challenges — making something work on a new hardware configuration where the path isn't obvious.
• Distributed systems research — solving concurrency / consistency problems where the field doesn't have an established answer.
• Bioinformatics, genuine scientific computation, robotics control.

What costs qualify

The claim process (briefly)

1. Identify qualifying R&D projects for the accounting period.
2. Compute qualifying expenditure (staff time × salary, plus other categories).
3. Write a project narrative — what was the advance sought, what uncertainty existed, what investigation was done, what was the outcome.
4. Submit alongside your CT600 corporation tax return — additional information form required as of 2023.
5. Wait. HMRC has up to 12 months to enquire. They increasingly do.

The advance-notification trap

Since April 2023, new claimants must notify HMRC of intent to claim within 6 months of the accounting period end. Miss this and the claim is invalid — you lose the year's relief entirely. Existing claimants (claimed within last 3 years) are exempt.

This catches a lot of founders. If you're thinking about claiming for the first time, file the notification proactively even before deciding to claim — it costs nothing and preserves the option.

Should you use a specialist?

For most early-stage tech startups, yes. The claim narrative is genuinely difficult to write defensively, the cost-apportionment requires judgement, and HMRC enquiries are a material risk. Typical specialist fee: 15-25% of the claim value (so on a £40k claim, you net £30-34k). That feels expensive until your claim gets challenged.

Red flags in specialists:

• "We'll claim 100% of your developers' time" — rarely true; HMRC scrutinises.
• Contingent fee with no fixed minimum — incentive is to claim aggressively.
• Won't share the narrative with you before submission.
• Promises a specific number before reviewing your projects.

Maintaining defensibility

Whatever you claim, HMRC's enquiry follows the trail back to your books and your development history. To make your books defensible:

• Tag R&D-relevant expenses consistently (a chart of accounts line for "R&D software" etc.)
• Keep time-tracking that shows the apportionment is rooted in reality, not retrofitted.
• Keep technical documentation (commit history, design docs, dead branches) that shows the uncertainty existed and was investigated.
• Don't backdate. Don't round.
• Keep your books reconciled and signed off monthly. A signed audit trail from before the claim was contemplated is the strongest evidence of good faith.

This is the part you read twice

This guide is educational. Do not file an R&D claim based on it alone.Rates, eligibility rules, and specifically which expenses qualify change frequently — the rules above are current at writing (May 2026) but HMRC issues guidance updates often, and the 2024 merged-scheme rules are still being interpreted in early enquiries. Engage an R&D specialist or your accountant before claiming. They will earn their fee.