R&D tax relief is one of the most valuable, most misunderstood instruments available to dual-jurisdiction startups. Done well, it returns 15 to 27 percent of qualifying spend in the UK and offsets meaningful payroll tax in the US. Done badly, it triggers HMRC enquiries and IRS Section 174 capitalisation surprises that wipe out your runway model.
The UK side: post-2024 merged scheme
HMRC's merged R&D Expenditure Credit applies to accounting periods starting on or after 1 April 2024. The headline rate is 20 percent above-the-line, with an enhanced 27 percent net for R&D-intensive loss-making SMEs (40%+ of total expenditure on qualifying R&D).
The US side: Section 174 capitalisation
Since the TCJA changes took effect, US R&E expenditure must be capitalised and amortised over five years (domestic) or fifteen years (foreign). For a UK-parented group with US developers, this creates a phantom taxable income problem even when the group is loss-making.
- Track engineering time by jurisdiction and by project from day one.
- Don't double-claim — UK qualifying expenditure cannot also be the basis for US R&D credit on the same payroll dollar.
- Use the US R&D payroll tax offset (up to $500k) before it becomes general business credit.
- Document contemporaneously. Retroactive timesheets fail HMRC enquiries.
Common traps
Misclassifying contractor spend, claiming for routine software development that doesn't meet the 'advance in science or technology' test, and missing the new overseas restriction on UK claims for non-UK contractors. Each of these has cost our clients six figures before we got involved.