Why this page exists
Almost everything published on this is written by a firm that wants your claim
That's not a criticism; it's just the market. But it means the honest version of "should I do this myself" barely exists anywhere, because it's not in anyone's commercial interest to write it. Established Finance isn't a claim-preparation firm. We're an introducer, so we don't have that conflict here. What follows is what self-filing actually involves, told straight.
What filing it yourself actually involves
Four things have to happen, in roughly this order
- Check whether you need to notify HMRC first. Some companies (generally first-time claimants, or those who haven't claimed in the last three years) must tell HMRC they intend to claim within six months of the end of the accounting period. See the three-year notification rule if you've claimed before but not recently. It catches more established companies than people expect.
- Write the technical narrative and identify the qualifying costs. This is the substantive work: explaining what the technical uncertainty was, how it was resolved, and working out which staff time, subcontractor costs, consumables and software genuinely relate to the qualifying work. See R&D claim services for the full mechanics of this step.
- Submit the Additional Information Form. It's mandatory for every claim, whoever prepares it, and has to reach HMRC before or on the same day as your Company Tax Return. Otherwise the claim isn't accepted at all. See the Additional Information Form for exactly what it needs, project by project.
- Submit the claim through your CT600. The relief is claimed on your Company Tax Return itself, supported by the Additional Information Form already on file.
None of this requires an agent. It requires someone in the business who can write clearly about a technical problem, and who's willing to deal with HMRC's paperwork directly rather than through an intermediary.
Worth knowing: advisers who interact with HMRC on a client's behalf now fall under a formal registration requirement under the Finance Act 2026, Part 7 (Schedule 20 sets out the exemptions to it, not the requirement itself). That requirement doesn't reach a company filing its own claim: there's no agent to register because there's no agent involved. It's a narrow point, but a real one: self-filing sidesteps a compliance question that instructing an adviser now raises.
When DIY genuinely fits
Four signs it's genuinely a fit, not just a way to save a fee
In our view, self-filing tends to work well when most of the following are true:
- The technical work is relatively contained and well-documented, not spread thinly across many small, ambiguous projects.
- Someone in the business (usually a technical lead or the FD) can write a clear, specific account of what the uncertainty was and how it was worked through, without falling back on vague, boilerplate language.
- The company is comfortable dealing with HMRC's forms and deadlines directly, and isn't relying on someone else to track the notification window.
- Records of the work already exist in some usable form (project notes, decision logs, version history), not just a tidy summary written after the fact. See evidence and records for an R&D claim for what that actually needs to look like.
When specialist help earns its fee
Paying for it isn't just the cautious option. It's sometimes the right one
Specialist help tends to be the better call when:
- The work sits close to the boundary of what qualifies: there's genuine uncertainty about whether it's R&D at all rather than routine engineering or software development.
- Nobody in the business has the time, or the writing confidence, to produce a specific technical narrative rather than a generic one. A narrative that could describe almost any project is a bigger risk than caution about doing it yourself.
- You want enquiry-defence support built into the arrangement from the start, rather than facing an HMRC compliance check alone if one comes.
- The claim is large enough, or complex enough across multiple projects, that the cost of getting it wrong clearly outweighs an adviser's fee.
Decision helper
What it costs either way
Self-filing costs time, not a fee, but weigh it against the fee anyway
That time is easy to understate. The fee comparison is worth having in front of you before deciding. Of the 17 firms in our own adviser register, only 5 publish a specific fee rate or model at all. Where a rate is disclosed, it runs from the mid-single-digit percentages on a tiered model up to 25% of the claim on a straightforward contingency basis, depending on size and structure (see the full fee comparison). That's the number to weigh against the time it takes to write a specific, well-evidenced narrative yourself.
Alternatives and limitations
This page is the overview. Two questions come up often enough to warrant their own pages: whether a small claim is worth the effort at all (is my R&D claim too small), and what "enough" evidence actually looks like (evidence and records for an R&D claim). If you'd rather not do this yourself, R&D claim services covers what a prepared claim involves, and the adviser register is a sourced starting point, not a recommendation.
