26 January 2026
Ask the Expert: Forms, Forms, Forms!
4 min read
HMRC’s R&D tax relief process now involves multiple mandatory forms. Learn which forms apply in 2026, key deadlines to watch, and how to avoid common mistakes.
26 January 2026
4 min read
HMRC’s R&D tax relief process now involves multiple mandatory forms. Learn which forms apply in 2026, key deadlines to watch, and how to avoid common mistakes.
What paperwork do you need for an R&D tax relief claim in 2026?
R&D tax relief is still a great incentive for UK businesses that invest in innovation. Recently, the claim process has become more structured and often involves more paperwork. To help explain what’s needed in 2026, we spoke with Mike Baker, Legal Manager at ABGi UK, about the forms required, why they matter, and how businesses can handle the process with confidence instead of frustration.
A: That’s because HMRC has tightened the process over the last few years to improve the quality and consistency of R&D claims. The intention isn’t to make claims harder for people, but to ensure HMRC receives the right information, in the right order, to assess whether a claim genuinely qualifies. Because of these changes, companies might need to submit up to four different forms or documents, depending on their situation. Each form has a specific purpose, and missing any required one can invalidate the whole claim, even if the rest is correct.
A: Not every company has to submit all four forms, but you must submit every form that applies to your case. If you miss a required form, your claim will fail, even if your numbers are right. It can be confusing, so I’ve created a simple chart below to show which form is needed at each stage of the process.
R&D Tax Relief Claim Forms in 2026
| Form | Required By | Stage in the Process | Why it is used / Circumstances |
| Claim Notification Form | New claimants (or those who haven’t claimed in 3 years). | Within 6 months after the end of the accounting period. | To inform HMRC of your intent to claim; failure to notify by this deadline prevents a claim later. |
| Additional Information Form (AIF) | All companies claiming R&D relief. | Must be submitted before (or on the same day as) the CT600. | Provides the technical narrative and project-by-project cost breakdowns. |
| CT600L (Supplementary Page) | All companies claiming under the Merged Scheme or ERIS. | Submitted with the Company Tax Return (CT600). | To calculate the payable credit amount, apply the PAYE/NIC cap, and set the credit against liabilities. |
| Company Tax Return (CT600) | All companies must submit their claim through their CT600. | Generally within 12 months of the end of the accounting period. | The main return where the final R&D figures are officially “made” as a claim. |
A: I want to leave you with the following 5 best practices, which I think will help.
1 | Master the Deadlines and Sequencing
HMRC is strict about submission timings.
➔ If you’re claiming for the first time, the Claim Notification Form is your most important deadline. If you miss the six-month window after your accounting period ends, you won’t be able to make a claim for that period.
➔ The AIF acts as a gatekeeper. You must submit it before or on the same day as your CT600. If HMRC processes your return without the AIF, your claim will be automatically rejected.
➔ Don’t rush the CT600. Even though you have a deadline for the main tax return, make sure all supplementary pages (CT600L) and the AIF are ready at the same time. Remember, you can’t pick and choose which parts to complete. If you miss any required part, your whole claim will be invalid.
2 | Keep records as you go
The forms require detailed input. The AIF, in particular, asks for project-by-project breakdowns.
✔ Track Costs as You Go: Do not try to reverse-engineer R&D expenditure at year-end. Have robust systems throughout the year to log staff time, materials, and subcontracted costs related to R&D.
✔ Keep evidence as you go. HMRC often audits claims and wants proof that R&D work happened when you say it did. Keep records like project plans, meeting notes, technical challenges, and failed experiments.
3 | Take the technical narrative seriously
HMRC uses the AIF narrative to assess whether work qualifies as R&D.
❌ Avoid “Buzzwords”:Clearly articulate the specific scientific or technological uncertainty you faced and how your R&D sought to resolve it.
✔ Get Technical Input:Ensure the person writing the AIF has sufficient technical knowledge of the projects.
4 | Be mindful of the PAYE/NIC cap calculation
For payable credits, the amount you can receive is generally capped at £20,000 plus 3 times your PAYE/NIC liability for relevant R&D staff. There are narrow exemptions, but these need to be justified.
5 | Consider professional advice
Because there are so many forms, strict deadlines, and close checks, many companies work with specialists to get the process right and lower the risk of rejection or enquiry.
A: Basically, the key is to step back and think about the process as a sequence, rather than a pile of forms. Once you understand the order and purpose of each step, it becomes much more manageable. If the forms feel daunting, that’s usually a sign that some early planning would help.
We hope Mike’s insights have been helpful – If you have any questions, please get in touch with ABGi , and a representative will get back to you to discuss your unique needs and explain how we can assist.