How to Submit an R&D Tax Credit Claim to HMRC: A Step-by-Step Guide for 2026–27
I once had a client tell me, quite cheerfully, that filing his R&D claim "took about an hour on a Sunday." He'd downloaded a template, filled in a few numbers, and submitted it. Eleven months later, he was still going back and forth with HMRC over a compliance check that, in the end, cost him more in advisory time than the relief itself had been worth. That's not a scare story to put you off claiming — R&D relief is genuinely one of the most valuable reliefs available to UK businesses, and it's there to be used. It's a story about why the process matters just as much as the eligibility.
If you read our earlier guide, "7 Mistakes to Avoid When Making an R&D Claim to HMRC in 2026–27", you'll know the scheme has changed substantially over the past couple of years, and HMRC now reviews around one in five claims — a level of scrutiny that simply didn't exist five years ago. That guide covered what goes wrong. This one is about doing it right the first time: a proper, step-by-step walk-through of how an R&D claim actually comes together, from working out whether you qualify through to submission and what happens afterwards.
Let's get into it.
Before anything else, you need to establish that what you're doing actually meets HMRC's definition of R&D for tax purposes — which is narrower, and more specific, than the everyday meaning of the phrase. The test has two core parts: your project must seek an advance in science or technology, and it must involve resolving genuine scientific or technological uncertainty — uncertainty that a competent professional in the field couldn't have readily resolved.
This is where I see the most confusion. Commercial risk isn't the same as technical uncertainty. A business wondering "will customers buy this?" isn't doing R&D. A business wondering "is it even technically possible to achieve this specification within these constraints?" might well be. I worked with a joinery business near Sevenoaks who'd developed a new jointing technique to solve a persistent warping problem in a particular timber. Nobody on the team thought of it as "research" — it was just solving a problem that had been bugging them for months. But the systematic experimentation involved, and the genuine uncertainty about whether it would work at all, meant it qualified.
Go through every project from the accounting period and ask honestly: was there real technical uncertainty here, or just the normal, everyday challenge of getting something built or built well? Be honest at this stage — inflating borderline projects is exactly the kind of thing that invites the scrutiny we covered in our mistakes guide.
For accounting periods beginning on or after 1 April 2024, most companies claim through the merged R&D scheme, which delivers a taxable credit worth 20% of qualifying expenditure. If your company is loss-making and your R&D spend represents at least 30% of your total expenditure, you may instead qualify for the Enhanced R&D Intensive Support scheme, ERIS, which can deliver a considerably more generous effective rate — up to around 27% of qualifying spend.
Work this out properly before you go any further, because it shapes everything downstream: how you calculate the claim, what rate applies, and even how you present your cost breakdown. I'd always recommend running the intensity calculation formally rather than estimating it, since companies sitting close to that 30% line can genuinely tip either way depending on exactly how costs are categorised.
This step catches out more businesses than any other, and it happens right at the start of the process, often before the accounting period has even ended. If you haven't claimed R&D relief in any of the previous three accounting periods, you're required to submit an Advance Notification Form to HMRC within six months of the end of the accounting period the claim will relate to. Miss that window, and HMRC can refuse to accept the claim entirely — regardless of how strong the underlying R&D case is.
Mark this date the moment you suspect a project might qualify, not once you're confident it does. It costs nothing to notify HMRC of a claim you later decide not to pursue, but it costs you the entire claim if you notify too late. If you're a first-time claimant, or you haven't claimed in the last three years, put this in the diary today.
With eligibility and scheme confirmed, the next job is working through your costs carefully. Qualifying expenditure generally includes:
A word of caution on two areas that trip people up constantly. First, overseas costs: under the current rules, payments to overseas subcontractors or externally provided workers are generally excluded unless you can demonstrate the work genuinely couldn't have been done in the UK — not that it was cheaper elsewhere, but that the necessary conditions simply weren't available here. Second, apportionment: if a member of staff spends 60% of their time on qualifying R&D and 40% on unrelated production work, only that 60% belongs in the claim, and you need a defensible, documented basis for that split — a rough guess won't hold up under review.
Build a clean spreadsheet, project by project, cost category by cost category. This isn't just good practice — it's exactly the evidence HMRC will expect to see if your claim is ever queried.
This is, in my experience, where the real quality gap between claims shows up. The technical narrative is your written case explaining, project by project, what the technological or scientific advance being sought was, what uncertainty existed, and what work was actually done to try to resolve it. A strong narrative doesn't read like a marketing brochure. It reads like an honest account of a genuinely difficult problem, written by someone who actually understood the technical detail — because, frankly, it should be.
For each project, aim to cover:
That fourth point matters more than people expect. Dead ends and failed approaches are often the clearest evidence of genuine uncertainty — a project that worked first time with no false starts is a much harder case to make than one with real trial and error behind it. Don't be embarrassed by the mess; it's often your best evidence.
Since August 2023, every R&D claim must be accompanied by a formal Additional Information Form, submitted to HMRC before your Company Tax Return, setting out your qualifying projects, the technical narrative for each, and a breakdown of costs by category. A claim submitted without this form attached is treated as invalid outright — not delayed, not queried, simply not accepted.
The form requires more detail than many businesses expect, including the name of the person responsible for the R&D and the agent involved, if any. Rushing this stage, or treating it as a formality after the "real work" of the technical narrative is done, is one of the fastest routes to triggering exactly the kind of enquiry we discussed in our mistakes guide.
Once the Additional Information Form is submitted, the R&D figures need to be reflected properly in your Company Tax Return, the CT600, including the relevant supplementary pages for R&D relief. This is where your qualifying expenditure translates into an actual reduction in corporation tax, or, for loss-making companies pursuing a payable credit, the calculation of the cash amount due — subject to the PAYE and NIC cap, which limits payable credits to £20,000 plus three times your total PAYE and NIC liability for the period.
Remember, too, that the standard time limit to claim R&D relief for a given accounting period is two years from the end of that period. If you're catching up on a prior year, check the calendar before assuming there's still time.
Once everything is filed, HMRC aims to process the majority of claims — around 85% — within 40 days, though a clean merged scheme claim more realistically tends to take somewhere in the region of eight to twelve weeks in current conditions. If your claim is selected for a compliance check, don't panic — a meaningful proportion of genuinely valid claims are reviewed as part of HMRC's now much broader compliance activity, not because something is necessarily wrong.
What matters, if that happens, is having the material ready to respond properly: the technical narrative, the cost workings, and a clear paper trail showing how each figure was reached. This is exactly why the quality of the work in Steps 4 and 5 pays off long after the claim has been submitted — a thin, rushed claim creates far more work later than a properly built one does at the outset.
I won't pretend every step above is beyond a capable business owner working carefully through it alone — plenty of our clients could, in principle, do most of this themselves. But in practice, the areas where claims most often go wrong are precisely the areas where specialist experience matters most: judging genuinely borderline technical uncertainty, correctly applying the overseas cost restrictions, choosing between the merged scheme and ERIS with confidence, and writing a technical narrative that reads as credible to someone at HMRC who reviews hundreds of these a year.
We work with businesses across Tunbridge Wells and the wider South East to handle exactly this — not simply filling in forms, but building a claim that's accurate, properly evidenced, and genuinely maximises the relief you're entitled to without straying into the kind of overreach that invites unwanted attention. Having sat on the other side of enquiry letters more times than I'd like, I can tell you the difference between a claim built properly the first time and one assembled in a rush on a Sunday afternoon is enormous — not in the paperwork, but in how the following twelve months actually go.
If you're preparing an R&D claim for this accounting period, or reviewing your approach after reading our guide on the mistakes that most often lead to rejection or enquiry, get in touch, and we'll help you build a claim you can stand behind with real confidence.
Disclaimer:
The content of this blog is for general informational purposes only and should not be considered professional tax advice. The information is correct at the time of publishing but may change following future UK budget announcements or updates to HMRC guidance. Individual circumstances vary, and tax obligations can differ based on your personal situation. We strongly recommend consulting with us or a qualified tax professional to receive advice tailored to your specific needs.
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