Short answer
It is a mandatory online form that has to reach HMRC before, or on the same day as, the company tax return containing an R&D claim. It sets out the company’s details, the qualifying costs broken down by category, and a technical narrative for the projects you are required to describe. Any R&D claim made on or after 8 August 2023 is invalid without one, whatever accounting period it relates to — and if the return goes in first, HMRC removes the claim from it.
Applies to
- Schemes
- Merged scheme · ERIS · Legacy SME
- Periods
- 1 April 2023 onwards
- Claimants
- All
What the form is and why it exists
The additional information form is an online submission that sets out the detail behind an R&D claim: who the company is, who prepared the claim, what it spent, and what the R&D actually was. Before August 2023 that material went to HMRC in whatever shape the adviser chose, or not at all. Now it goes in a fixed structure, and the claim is invalid without it.
The requirement is defined by the date the claim is made, not by the accounting period. A claim for a 2021 accounting period filed today needs a form in exactly the same way as a claim for the current year.
When it has to be submitted
Before the company tax return, or on the same day as it. If the two go on the same day, the form must go first.
If the return arrives before the form, HMRC treats the claim as invalid and removes it from the return. This is not a warning letter and a chance to fix it; the claim comes out. Where the time limit for the period has not passed, the claim can be made again — form first this time. Where it has passed, it is gone.
That makes the sequence the single most important administrative fact about an R&D claim. Filing software will let you submit a return with the R&D boxes completed whether or not a form has been sent, so nothing stops the wrong order happening.
What it asks for
- The company. Registered name, unique taxpayer reference, PAYE reference, VAT registration number and the SIC code for the trade.
- Contacts. The senior internal contact responsible for the claim, and every agent involved in it. “Every agent” means what it says: where a general practice accountant files the return and a specialist prepares the claim, both go on the form.
- The period. The start and end dates of the accounting period, which must match the tax return exactly.
- The costs. Qualifying expenditure broken down by category, split between amounts brought into account under generally accepted accounting practice, pre-trading expenditure and expenditure capitalised as an intangible asset.
- Intensity information, where enhanced R&D intensive support is being claimed — the company’s total relevant expenditure, and that of connected companies.
- The projects. The number undertaken, and a narrative for each project you are required to describe.
For each project the form asks for the field of science or technology, the level of knowledge or capability that existed when the project started, the advance the project sought, the scientific or technological uncertainties faced, how the company tried to resolve them, and the qualifying expenditure attributed to that project.
Those six questions are the statutory definition of R&D restated as a form. They are covered in How do I know if I’m doing R&D? and What is a scientific or technological uncertainty?.
Which projects you have to describe
You do not always have to describe all of them. The rule turns on how many projects the claim covers.
| Number of projects in the claim | What must be described | Note |
|---|---|---|
| One to three | All of them | Every project is a relevant project |
| Four to ten | At least three, together covering at least half the qualifying expenditure | Take them in descending order of cost and stop when you pass half |
| Eleven or more | At least three, together covering at least half the qualifying expenditure — but never more than ten | If ten projects still do not reach half, describe the ten largest and stop |
The selection is arithmetic, not editorial. You work down the projects by qualifying expenditure until the ones you have selected account for half the total.
Who submits it
An officer of the company, or an agent with an agent services account. Each company in a group needs its own Government Gateway credentials to submit its own form — a group cannot file one form covering several companies, and it cannot file its subsidiaries’ forms from the parent’s account.
Getting those credentials in place takes time that nobody has allowed for. On a group claim it is worth starting before the numbers are final.
Amended claims
The requirement attaches to the claim, and a claim can be amended as well as made. Where an amendment changes the claim — different costs, a different scheme, projects added or removed — a fresh form reflecting the amended claim should go in before the amended return. The legislation requires the information to have been provided no later than the date the claim is made or amended.
The form is a risk assessment tool
HMRC uses the form to decide where to look. A form whose project narratives describe commercial problems rather than technological ones, whose costs do not reconcile to the return, or which answers a question by pointing at an attached report, is more likely to attract an enquiry than one that does not. Cross-references to a separate R&D report are not accepted as answers; the form has to stand on its own.
Worked example
Illustrative. A company claims for twelve R&D projects in the year, with total qualifying expenditure of £1,000,000. Because there are eleven or more projects, it must select at least three projects that together account for at least half of that — £500,000 — and it will never have to describe more than ten.
| Project | Qualifying expenditure | Running total |
|---|---|---|
| Project 1 | £180,000 | £180,000 |
| Project 2 | £150,000 | £330,000 |
| Project 3 | £120,000 | £450,000 |
| Project 4 | £90,000 | £540,000 |
Four projects take the company past £500,000, so four narratives are required and the remaining eight projects are not described. Their costs still form part of the claim and still appear in the cost breakdown — the selection rule governs what has to be written up, not what can be claimed.
Reverse the figures and the answer changes. If the twelve projects were of roughly equal size at about £83,000 each, it would take seven of them to pass half, and seven narratives would be required.
Where claims go wrong
- The return goes in first. Usually by minutes, and usually because two different people are pressing two different buttons. The claim is removed, and where the time limit for the period has already passed there is no way back. Anyone filing a return with R&D boxes completed should have the form’s submission confirmation in front of them before they file.
- Answering a question with “see the R&D report”. The form has to be self-contained. A cross-reference is treated as no answer, which puts the validity of the claim in play as well as inviting an enquiry.
- Choosing the projects that are easiest to write about. The selection rule is a calculation on qualifying expenditure. Describing three tidy projects that between them account for a fifth of the claim does not satisfy it, and it leaves the largest costs in the claim undescribed — which is exactly the shape HMRC looks for.
- Describing commercial difficulty as technological uncertainty. A tight budget, an immovable customer deadline or an unfamiliar tool are not scientific or technological uncertainties. This is the most common substantive weakness in the narratives we see, and the form is where it becomes visible.
- Group logistics left to the end. Every company in a group needs its own Government Gateway account to file its own form. Discovering that in the last week before a deadline, across six subsidiaries, is a filing risk created entirely by administration.
- The numbers not agreeing. The cost breakdown on the form, the figures on the CT600L and the schedules behind the claim should reconcile exactly. Where they do not, the discrepancy is the first thing an officer asks about.
John Mapother
Founder & Director
Last reviewed 1 September 2026