- R&D tax credits reward UK limited companies for resolving scientific or technological uncertainty, and the relief is claimed through the Company Tax Return.
- Every claim must include an Additional Information Form before the CT600, and most first-time claimants need to file a Claim Notification Form within six months of the accounting period end.
- Claims must usually be submitted within two years of the end of the accounting period, and failed projects can still qualify if they genuinely tried to overcome technical uncertainty.
Knowing how to claim R&D tax credits in the UK starts with identifying qualifying projects, calculating eligible costs, and submitting an Additional Information Form before your Company Tax Return. Most companies have up to two years from the end of the accounting period to make a claim, and the tax saving can be substantial.
The rules changed for accounting periods starting on or after 1 April 2024 under the merged scheme, so getting the structure right matters more than ever.
If you are weighing up whether your work qualifies for Sleek’s R&D tax credit support, would you rather spend weeks deciphering HMRC’s rules or have specialists handle the claim for you?
What are R&D tax credits in the UK?
R&D tax credits are a corporation tax incentive that rewards UK companies for resolving scientific or technological uncertainty in their work. They reduce the tax bill of profitable companies and can deliver a payable cash credit to loss-makers, depending on which scheme applies.
The relief sits inside the broader corporation tax framework, so the value of any claim depends on profits, scheme rules, and the current corporation tax rate. HMRC reformed the system in April 2024 by merging the SME and RDEC schemes for most claimants, while keeping a separate Enhanced R&D Intensive Scheme (ERIS) for loss-making R&D-intensive SMEs.
Companies use the relief to fund further development, hire technical staff, and reinvest in product or process improvements. It is available across every sector, provided the work meets HMRC’s definition of R&D.
Who qualifies for R&D tax relief in 2026?
A project qualifies for R&D tax relief when it seeks an advance in science or technology by resolving uncertainty that a competent professional could not easily work out. Eligibility is based on the nature of the work, not the industry, so software firms, manufacturers, food producers, and engineering businesses can all claim.
The competent professional test is central. HMRC expects you to show that someone qualified in the field could not deduce the solution from publicly available information without testing or experimentation.
You must be a UK limited company that is registered for corporation tax and trading. Sole traders and general partnerships are not eligible. Failed projects still qualify if they genuinely attempted to overcome technical uncertainty, which is one of the most overlooked rules in the relief.
Which scheme applies to your claim?
The scheme you use depends on when your accounting period started and whether you are a loss-making R&D-intensive SME. For accounting periods beginning on or after 1 April 2024, most companies fall under the merged scheme, while loss-making SMEs spending at least 30% of total expenditure on R&D may qualify for ERIS.
Earlier accounting periods still use the legacy SME scheme or the legacy RDEC route depending on company size. The differences affect the rate of relief, how the credit is paid, and how the figures are entered on the CT600.
Scheme | Who it applies to | Period it covers |
Merged R&D Expenditure Credit | Most UK companies | Accounting periods starting on or after 1 April 2024 |
Enhanced R&D Intensive Scheme (ERIS) | Loss-making SMEs with 30% or more R&D spend | Accounting periods starting on or after 1 April 2024 |
Legacy SME scheme | Small and medium-sized enterprises | Accounting periods before 1 April 2024 |
Legacy RDEC | Large companies and grant-funded SMEs | Accounting periods before 1 April 2024 |
What costs can you include in an R&D claim?
Qualifying R&D costs are expenses directly tied to resolving scientific or technological uncertainty in your project. HMRC will not accept overheads such as rent, marketing, or general administration unless they are a clear consumable input to the R&D itself.
The most common qualifying categories are:
- Staff costs covering salaries, employer NICs, and pension contributions for those working on R&D
- Externally provided workers and subcontractors carrying out R&D activity
- Software, cloud computing, and data licence costs used directly in R&D
- Consumables such as materials, fuel, and utilities used up during the R&D
- Payments to volunteers in clinical trials
- A portion of allowable limited company expenses where they directly support the qualifying activity
You can apportion costs where staff or resources split time between R&D and non-R&D work, but the apportionment must be reasonable and well documented. Records should be kept as the work happens, not reconstructed at year-end.
How do you claim R&D tax credits step by step?
The claim process runs through your Company Tax Return, but it now requires extra HMRC forms before you file. Missing any deadline can invalidate the entire claim, so the order matters.
- Identify qualifying projects and document the technical uncertainty each project tried to overcome.
- Calculate qualifying costs across staff, subcontractors, software, and consumables for the accounting period.
- Submit a Claim Notification Form within six months of the accounting period end if it is your first claim or you have not claimed in the last three years.
- Complete and submit the Additional Information Form detailing projects, costs, and the competent professional behind the claim.
- File the CT600 Company Tax Return with the R&D claim entered in the correct boxes, including box 657 to confirm AIF submission.
- Settle any related liability through your usual corporation tax payment route if there is a balance due after the credit is applied.
Submit the Claim Notification Form even if you are not sure the claim will go ahead. The form is free, low effort, and missing the six-month window blocks the entire claim no matter how strong the project is.
When are the deadlines for an R&D tax claim?
You usually have up to two years from the end of the accounting period to make a claim, but other deadlines feed into that window. The Claim Notification Form has a much shorter timeframe and is the most common reason claims are rejected outright.
Form or step | Deadline |
Claim Notification Form (first-time or returning claimants) | Within 6 months of the end of the accounting period |
Additional Information Form | Before the CT600 is filed |
CT600 with R&D claim included | Within 2 years of the end of the accounting period |
Amending a previously filed CT600 to add a claim | Within 2 years of the end of the accounting period |
Companies with multiple accounting periods open at the same time should track each one separately, especially during the transition between legacy and merged scheme rules.
Common mistakes to avoid when claiming R&D tax credits
The most expensive mistakes happen before any tax form is touched. Weak project narratives, poor cost records, and missed notification windows can wipe out a valid claim before HMRC has even reviewed it.
- Treating routine product improvements as R&D, which is one of the fastest ways to trigger an HMRC enquiry
- Forgetting the Claim Notification Form when it is needed, which makes the claim invalid however strong the project is
- Claiming for ineligible costs such as land, capital expenditure on equipment, and pure marketing spend
- Confusing R&D tax credits with other reliefs such as SEIS and EIS investment incentives or Business Asset Disposal Relief for entrepreneurs, which target different activities entirely
- Submitting a vague Additional Information Form that does not name the competent professional or describe the technical uncertainty in clear terms
- Reconstructing time records months after the work happened, instead of tracking R&D time as it is incurred
How Sleek helps with R&D tax credit claims
Sleek’s accountants prepare the technical narrative, calculate qualifying costs, and submit every HMRC form on your behalf, so the claim reaches HMRC in the right shape and on time. We work with limited company founders across software, engineering, and life sciences, and we handle both new and returning claimants under the merged scheme and ERIS.
If your accounting period is approaching, we can confirm your eligibility, prepare the Claim Notification Form, and pull the financial data straight from your books. Our R&D tax credit specialists handle the entire process, leaving you free to focus on the work the relief was designed to reward.
Disclaimer: The preceding information is not legal advice. This content is aimed to provide general guidance. For more formal or legal advice, contact Sleek directly.
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FAQs on how to claim R&D tax credits in the UK
How much can you claim for R&D tax credits?
Under the merged scheme (accounting periods starting on or after 1 April 2024), the credit rate is 20% of qualifying expenditure, applied against your corporation tax liability. Loss-making R&D-intensive SMEs using ERIS receive a 27% credit rate. Under the legacy SME scheme, profitable companies reduced taxable profits by 130% of qualifying costs, while loss-makers could surrender losses for a cash payment of up to 33p per pound spent.
Can startups claim R&D tax relief?
Yes. Startups can claim provided they are incorporated as a UK limited company and registered for corporation tax. Loss-making startups are common in R&D-intensive sectors, and both the merged scheme and ERIS allow for payable credits rather than just a tax reduction. The Claim Notification Form deadline is especially critical for first-time claimants. Sleek’s startup accounting service can help you file before the window closes.
What evidence do you need for an R&D claim?
You need project-level documentation describing the scientific or technological uncertainty you tried to resolve, evidence of the competent professional overseeing the work, and contemporaneous cost records covering staff time, subcontractor invoices, and software licences. The Additional Information Form requires this in structured form before the CT600 is filed. Weak or retrospective documentation is one of the leading causes of HMRC enquiries into R&D claims.
How long does an R&D tax claim take?
HMRC typically processes straightforward claims within 28 days of a completed CT600 with an AIF already on file. Complex claims or those involving compliance checks can take several months. Preparation time before submission depends on the quality of your records. Companies with organised cost tracking and clear project notes can usually turn around the claim within two to four weeks.
How do you write a technical narrative for an R&D claim?
A technical narrative explains the scientific or technological uncertainty your project faced, why a competent professional could not resolve it without experimentation, and what approach your team took to overcome it. Write it from the perspective of someone with technical expertise in the relevant field, not as a general business description. Avoid vague terms such as “innovative” without explaining the specific uncertainty you were resolving.
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What happens after you submit an R&D claim?
HMRC processes the claim and either applies the credit to your corporation tax liability or issues a repayment where the credit exceeds it. In some cases HMRC opens a compliance check to verify the technical content or cost calculations. Responding promptly with clear documentation is the fastest way to close a compliance check and receive the credit. Most straightforward claims are resolved without any further contact.
What are HMRC R&D compliance checks?
HMRC compliance checks are formal reviews where HMRC queries the technical content, eligible costs, or scheme eligibility of a claim. They can be triggered by unusual claim values, an incomplete AIF, or sector-wide targeting. During a check, HMRC may request project records, cost breakdowns, and the technical narrative. Most checks resolve within a few months, but complex multi-year claims without clear contemporaneous records can take considerably longer.
