If your limited company has spent money developing a new product, process, or software, you could be owed tens of thousands of pounds from HMRC. R&D tax credits are not a niche relief for scientists in white coats. They apply to businesses across every sector, from a precision engineering firm in Sheffield's Kelham Island to a fintech startup in London's Shoreditch. This is r&d tax credits explained from first principles to the 2025/26 rules, written for directors who need to know what qualifies, what doesn't, and how to claim without triggering an HMRC enquiry.

As ICAEW qualified accountants working with UK businesses of every shape, we see claims fail for three reasons: poor documentation, misunderstanding what qualifies, and missing the deadline. This guide eliminates all three risks. It covers the merged R&D scheme that applies from 1 April 2024, the Enhanced R&D Intensive Scheme (ERIS) for loss-making companies, and the practical steps to build a defensible claim.

What Are R&D Tax Credits?

R&D tax credits are a government relief designed to reward UK companies that invest in research and development. They reduce your corporation tax bill or, if your company is loss-making, provide a cash payment from HMRC.

The relief exists because innovation is expensive and risky. HMRC accepts that not every R&D project succeeds. What matters is that you attempted to resolve scientific or technological uncertainty. The definition is deliberately broad, and it covers more activities than most directors realise.

Who Can Claim R&D Tax Credits?

Only limited companies can claim R&D tax credits. Sole traders, partnerships, and LLPs cannot. The company must be within the charge to UK corporation tax, and the R&D activity must take place in the UK, though some overseas costs can qualify in limited circumstances.

There is no minimum spend. We have seen valid claims for companies spending as little as £10,000 on qualifying costs. There is also no upper limit, though claims above £2m attract additional HMRC scrutiny.

The Two Pre-Merger Schemes (Historical Context)

Before 1 April 2024, there were two separate R&D schemes:

  • SME R&D Relief, for companies with fewer than 500 employees and either turnover under €100m or a balance sheet under €86m. This provided an enhanced deduction of 186% (previously 230% before April 2023) and a payable credit of up to 14.5% for loss-making companies.
  • R&D Expenditure Credit (RDEC), for large companies and SMEs that had been subcontracted to do R&D work. This provided a 20% above-the-line credit (previously 13% before April 2023).

The distinction caused confusion, particularly for companies that grew beyond the SME thresholds mid-project. The merged scheme simplifies this.

The Merged R&D Scheme (From 1 April 2024)

For accounting periods beginning on or after 1 April 2024, the SME and RDEC schemes have been merged into a single regime. This is the biggest change to R&D tax relief in a decade, and it affects every company that claims.

Scheme Accounting periods starting before 1 April 2024 Accounting periods starting on or after 1 April 2024
SME R&D Relief (enhanced deduction) 186% (loss-making: 14.5% payable credit) Merged into single scheme
RDEC (large companies) 20% credit (13% pre-April 2023) Merged into single scheme
New merged scheme N/A 20% credit for all companies (19% for loss-making)
ERIS (intensive R&D) N/A 27% credit (loss-making SMEs with 30%+ R&D intensity)

How the Merged Scheme Works

Under the merged scheme, all companies receive an above-the-line credit of 20% of qualifying R&D expenditure. This credit is treated as income for corporation tax purposes. The net benefit depends on whether your company is profit-making or loss-making.

For a profit-making company, the 20% credit reduces your corporation tax liability. The effective net benefit after tax is approximately 15% to 16%, depending on your corporation tax rate.

For a loss-making company, the credit can be surrendered to HMRC in exchange for a cash payment. The payable credit rate is 19% of the surrendered loss, capped at the company's total PAYE and NIC liabilities (the "PAYE cap").

The PAYE Cap

From 1 April 2024, the amount of payable credit a loss-making company can receive is capped at the lower of:

  • £20,000 plus 300% of the company's total PAYE and NIC liabilities for the period, or
  • The total amount of the credit itself.

This cap primarily affects companies that outsource most of their R&D work. If your company has minimal payroll but significant subcontractor costs, the PAYE cap may restrict your claim. We discuss this in more detail under R&D tax credits.

What Qualifies as R&D for Tax Purposes

HMRC defines R&D as work that seeks to achieve an advance in science or technology. The advance must be in the field of your business, not just an advance for your company. However, the bar is lower than most directors think.

The Four-Part Test

HMRC applies a four-part test to determine whether work qualifies:

  1. Advance, Did the project seek to achieve an advance in science or technology?
  2. Uncertainty, Was there scientific or technological uncertainty at the start that competent professionals in the field could not easily resolve?
  3. Resolution, Did the project attempt to overcome that uncertainty?
  4. Competent professional, Would a competent professional in the field recognise the uncertainty as genuine?

If you answer yes to all four, the work likely qualifies. The advance does not need to be world-changing. Adapting an existing technology to a new use, where the outcome is not predictable, can qualify.

Qualifying Costs

The following costs can be included in an R&D claim:

  • Staff costs, Salaries, wages, employer's NI, and pension contributions for employees directly involved in R&D. This includes directors who work on R&D projects.
  • Subcontractor costs, Payments to subcontractors doing R&D work on your behalf. The amount you can claim depends on whether the subcontractor is connected to you.
  • Consumables, Materials, energy, water, and other consumables used directly in R&D. Software licenses used for R&D also qualify.
  • Externally provided workers, Staff provided by an agency or employment business, subject to certain conditions.
  • Contributions to independent research, Payments to universities or research organisations for R&D work.

What Does Not Qualify

Several common costs are excluded:

  • Capital expenditure (though you may claim capital allowances separately)
  • Land and buildings
  • Routine data collection or market research
  • Routine testing without scientific or technological uncertainty
  • Work funded by grants or subsidies (unless the grant is specifically for R&D)
  • Production or commercialisation costs

Worked Example: Precision Components Ltd

Precision Components Ltd is a manufacturing company based in Sheffield's Kelham Island. It has 12 employees and develops a new alloy for aerospace components. The project takes 14 months and costs £147,800 in qualifying R&D expenditure.

Staff costs: Two engineers working 60% of their time on the project. Combined salary £63,400, employer's NI £8,620, pension contributions £3,800. Total staff cost: £75,820.

Consumables: Specialist metals, testing materials, and energy costs directly attributable to the R&D: £38,200.

Subcontractor costs: A materials testing lab in Manchester's MediaCity charged £33,780 for testing services. The subcontractor is unconnected.

Total qualifying R&D expenditure: £147,800.

Precision Components Ltd is profit-making and pays corporation tax at 25%. Under the merged scheme:

  • R&D credit: 20% × £147,800 = £29,560
  • The credit is treated as income, so it increases taxable profits by £29,560
  • Additional corporation tax due on the credit: 25% × £29,560 = £7,390
  • Net benefit to the company: £29,560 − £7,390 = £22,170

If Precision Components Ltd were loss-making, the calculation would differ. The payable credit would be 19% of the surrendered loss, subject to the PAYE cap.

The Enhanced R&D Intensive Scheme (ERIS)

The merged scheme includes a special provision for loss-making SMEs that are "R&D intensive". This is known as the Enhanced R&D Intensive Scheme, or ERIS.

Who Qualifies for ERIS

To qualify for ERIS, a company must meet all of the following conditions:

  • Be an SME (fewer than 500 employees, turnover under €100m or balance sheet under €86m)
  • Be loss-making (the company's R&D expenditure exceeds its income)
  • Have qualifying R&D expenditure that is at least 30% of its total expenditure
  • Be within the charge to UK corporation tax

The 30% intensity test is based on total expenditure, which includes cost of sales, administrative expenses, and other operating costs. Companies that spend heavily on R&D relative to their overall cost base are the most likely to qualify.

How ERIS Works

Under ERIS, the payable credit rate is 27% of the surrendered loss, compared to 19% under the standard merged scheme. This is a significant uplift for genuinely R&D-intensive companies.

Example: A biotech startup in Cambridge spends £340,000 on R&D and has total expenditure of £980,000. Its R&D intensity is 34.7%, above the 30% threshold. The company is loss-making and surrenders its entire R&D loss for a payable credit of 27% × £340,000 = £91,800, subject to the PAYE cap.

How to Make an R&D Tax Credit Claim

Making a claim requires more than just numbers. HMRC expects a detailed technical report explaining the R&D projects, the scientific or technological uncertainties, and how the qualifying costs were calculated.

The Technical Report

Every claim must be accompanied by a technical narrative that covers:

  • What the project aimed to achieve
  • The scientific or technological uncertainties that existed at the start
  • How the project attempted to overcome those uncertainties
  • What was actually achieved (even if the project failed)
  • The names and roles of the key technical staff involved

The report should be written in plain English, not technical jargon. HMRC assessors are not necessarily specialists in your field. They need to understand the advance and the uncertainty without being a metallurgist or a software engineer.

The Financial Report

The financial report breaks down the qualifying costs by category and explains how each cost was calculated. It should include:

  • Total qualifying R&D expenditure
  • Breakdown by cost category (staff, consumables, subcontractors, etc.)
  • Methodology for apportioning staff time
  • Basis for allocating consumables
  • Details of any connected party subcontractor costs

Filing the Claim

R&D tax credit claims are made through the company's corporation tax return (form CT600). The claim must be made within two years of the end of the accounting period. For example, for a company with a 31 December 2024 year-end, the claim must be filed by 31 December 2026.

Claims can be made by amending a previously filed CT600, but this must also be done within the two-year window. Late claims are not accepted.

The Additional Information Form

From 1 April 2024, all R&D claims must be accompanied by an Additional Information Form (AIF). This is a digital form submitted to HMRC before or at the same time as the CT600. The AIF requires:

  • Details of the R&D projects
  • Qualifying expenditure by category
  • Details of any subcontractors or externally provided workers
  • Confirmation that the company has not received grant funding for the same costs
  • Contact details of the person preparing the claim

HMRC uses the AIF to triage claims for enquiry. Incomplete or inconsistent AIFs are a red flag.

Common Mistakes and HMRC Enquiries

R&D tax credit claims are a high-priority area for HMRC. The number of enquiries into R&D claims has increased sharply since 2023. HMRC is particularly focused on claims that appear inflated, poorly documented, or made by companies that do not appear to be doing genuine R&D.

Mistake 1: Claiming for Routine Development

Not every improvement qualifies as R&D. If your company updated an existing product using known techniques and the outcome was predictable, it does not qualify. The key question is whether there was genuine scientific or technological uncertainty at the outset.

Mistake 2: Including Non-Qualifying Costs

Common errors include including marketing costs, routine software maintenance, and general administrative overheads. These are not qualifying costs and including them risks the entire claim being rejected.

Mistake 3: Poor Time Apportionment

Staff costs must be apportioned based on the actual time spent on R&D. Using rough estimates or claiming 100% of a director's salary when they spend significant time on non-R&D activities will trigger questions. HMRC expects a clear methodology, such as timesheets or project diaries.

Mistake 4: Missing the PAYE Cap

Loss-making companies that outsource R&D work often find their payable credit capped by the PAYE cap. This is not a mistake in the sense of an error, but it is a common source of disappointment. Companies should model their claim before filing to understand the cap's impact.

What Happens During an HMRC Enquiry

If HMRC opens an enquiry into your R&D claim, they will request the technical and financial reports, the AIF, and supporting documentation. They may ask for timesheets, project plans, technical specifications, and correspondence with subcontractors.

The enquiry process can take six to twelve months. Having robust documentation from the start is the best defence. We cover this in more detail on our R&D tax credits blog.

R&D Tax Credits for Software Companies

Software development is one of the most common areas for R&D claims, and one of the most misunderstood. HMRC has issued specific guidance on what qualifies in the software context.

What Qualifies in Software

Software R&D typically involves:

  • Developing new algorithms or mathematical models
  • Creating new programming languages or compilers
  • Developing new methods of data processing or analysis
  • Creating new approaches to security or encryption
  • Developing new methods of user interaction that require significant technical problem-solving

What Does Not Qualify in Software

Routine software development does not qualify. This includes:

  • Building a standard website or e-commerce platform using existing frameworks
  • Customising off-the-shelf software
  • Routine bug fixing or performance optimisation
  • Integrating standard APIs
  • Developing mobile apps that do not involve genuine technical uncertainty

The key test is the same as for any other sector: was there scientific or technological uncertainty that a competent professional could not easily resolve? If you are simply applying known techniques to a new problem, it is unlikely to qualify.

R&D Tax Credits and Grants

If your company has received grant funding, the R&D claim is affected. The general rule is that you cannot claim R&D tax credits on costs that have been funded by a grant. However, there are exceptions.

Notified vs Non-Notified Grants

HMRC distinguishes between notified and non-notified grants. A notified grant is one that is state aid approved and notified to the European Commission (or, post-Brexit, the UK's subsidy control regime). Non-notified grants are typically smaller, local authority grants.

If you receive a notified grant for a specific R&D project, the costs of that project cannot be included in an R&D claim. If you receive a non-notified grant, the position is more complex, and you may be able to claim R&D relief on the costs not covered by the grant.

Smart Grants and Innovate UK

Innovate UK Smart Grants and similar competitive grants are typically notified state aid. If your company wins a Smart Grant for an R&D project, you cannot claim R&D tax credits on the same costs. However, you may be able to claim on related costs that fall outside the grant-funded project.

Always check the terms of your grant agreement before making an R&D claim. Getting this wrong can result in HMRC clawing back the credit plus interest and penalties.

Action Checklist for Making an R&D Claim

Use this checklist to prepare and submit a defensible R&D tax credit claim. Tick off each item before filing.

  • Identify qualifying projects. Review all projects undertaken in the accounting period. Apply the four-part test to each one.
  • Document the technical uncertainty. Write a narrative for each project explaining the advance sought and the uncertainty faced. Do this before you submit the claim.
  • Calculate qualifying costs. Pull staff costs, consumables, subcontractor costs, and externally provided worker costs from your accounting records. Use actual figures where possible.
  • Apportion staff time. Use timesheets, project diaries, or a clear methodology to allocate staff time to R&D projects. Document the methodology.
  • Check the PAYE cap. If your company is loss-making, calculate the PAYE cap and model the impact on your payable credit.
  • Check for grants. Review all grant agreements to ensure no double-counting of costs.
  • Complete the Additional Information Form. Submit the AIF to HMRC before or alongside the CT600.
  • File the CT600. Include the R&D claim in the corporation tax return. Ensure the figures in the AIF match the CT600.
  • Keep records. Retain all supporting documentation for at least six years. HMRC can open an enquiry up to 12 months after filing.
  • Review annually. R&D is not a one-off exercise. Review each accounting period for qualifying projects.

If you are unsure about any step, speak to a qualified accountant who specialises in R&D claims. The cost of getting it wrong, a full HMRC enquiry, potential penalties, and reputational damage, far outweighs the cost of professional advice. Contact our team for a confidential discussion about your R&D claim.

For more detailed guidance, visit our R&D tax credits service page or read our R&D tax credits blog for updates on legislation and HMRC practice.