Research & Development (R&D) Tax Credits on CT600: SME Guide 2026

Research & Development (R&D) Tax Credits on CT600: SME Guide 2026

If your limited company develops new products, processes, or services — or improves existing ones — you may be leaving thousands of pounds on the table. R&D tax credits are one of the most valuable but underused reliefs available to UK companies, and claiming them on your CT600 can slash your corporation tax bill or even generate a cash payment from HMRC.

But the R&D landscape has changed dramatically. The merged R&D scheme (effective from April 2024) replaced the old SME and RDEC schemes, and HMRC compliance checks have surged. Getting your CT600 R&D claim right has never been more important — or more complex.

This guide covers everything a UK limited company needs to know about claiming R&D tax credits on the CT600 in 2025/26: qualifying expenditure, the merged scheme rates, how to complete the CT600 and CT600L supplementary page, HMRC compliance requirements, and whether to take a cash credit or tax reduction.

What Are R&D Tax Credits?

R&D tax credits are a government incentive that rewards UK companies for investing in innovation. If your company spends money on research and development activities, you can claim additional tax relief on that expenditure.

The core concept: Your company does R&D → you incur costs → you claim enhanced relief on those costs → your corporation tax bill decreases (or you receive a cash payment).

R&D tax credits are governed by Part 13 of the Corporation Tax Act 2009 (as amended by the Finance Act 2024) and the BEIS Guidelines on the Meaning of Research and Development.

Important: R&D tax credits are not just for tech companies. Any limited company in any sector that seeks to resolve scientific or technological uncertainty can qualify — from software developers to manufacturers, from food producers to construction firms.

The Merged R&D Scheme (From April 2024)

From accounting periods beginning on or after 1 April 2024, the old SME R&D scheme and the large company RDEC (Research & Development Expenditure Credit) scheme were merged into a single scheme — the merged R&D scheme.

Key Rates for 2025/26

How the Merged Scheme Works

1. Your company incurs qualifying R&D expenditure of, say, £100,000
2. You claim an additional deduction of 86% = £86,000
3. Your total deduction is £186,000 (the original £100,000 plus the £86,000 enhancement)
4. Tax saving at 25% = £186,000 × 25% = £46,500 (less the tax you'd have saved anyway on the £100,000, so the net benefit of the R&D relief is £86,000 × 25% = £21,500)

For loss-making companies, the mechanics are different — see the "Cash Credit vs. Tax Reduction" section below.

R&D Intensive Companies — Enhanced Rate

If your company is an SME and qualifies as "R&D intensive" (R&D expenditure represents 30% or more of your total expenditure), you may be eligible for the enhanced R&D intensive regime:

• Credit rate: 27% of surrenderable loss
• This replaces the standard merged scheme credit for qualifying loss-making R&D-intensive SMEs
• Available for accounting periods beginning on or after 1 April 2024

To qualify, your company must:

• Be an SME (fewer than 500 employees, turnover under €100M or balance sheet under €86M)
• Have qualifying R&D expenditure equal to at least 30% of total expenditure
• Be loss-making (or have losses attributable to R&D)

What Qualifies as R&D?

This is the question that trips up most companies. HMRC uses a specific definition based on the BEIS Guidelines, not the everyday meaning of "research and development."

The HMRC Definition

To qualify as R&D, a project must seek to achieve an advance in science or technology by resolving scientific or technological uncertainty.

Advance in science or technology means:

• Extending overall knowledge or capability in a field of science or technology
• Not just your company's knowledge — it must be an advance beyond what's generally available to competent professionals in the field

Scientific or technological uncertainty means:

• Whether something is scientifically possible or technologically feasible is not readily deducible by a competent professional
• It's not enough that the solution is merely difficult — there must be genuine uncertainty about how to achieve it

What Qualifies — Examples

Software development:

• Developing a new algorithm to solve a problem that existing methods can't handle efficiently
• Building a system that integrates technologies in a novel way where the outcome is uncertain
• Creating AI/ML models where the approach and architecture are unproven
• Overcoming technical challenges in scaling, performance, or reliability

Manufacturing:

• Developing a new production process that hasn't been achieved before
• Adapting existing processes to work with new materials where outcomes are uncertain
• Achieving tolerances or specifications beyond current industry capability

Engineering:

• Designing structures or systems that push beyond established design practices
• Developing new testing methodologies where existing approaches are inadequate

Life sciences:

• Developing new formulations, compounds, or biological processes
• Clinical trials and testing of new products

What Does NOT Qualify

• Routine development — building a website, app, or system using established techniques with no technical uncertainty
• Cosmetic or aesthetic improvements — changing the design or look of a product
• Market research — researching customer needs or market opportunities
• Social sciences — economics, business studies, management theory
• Arts and humanities — creative writing, design (unless combined with technological uncertainty)
• Simply using existing technology — implementing off-the-shelf software, following standard procedures

Not sure if your work qualifies? HMRC's advance assurance service lets first-time claimants get confirmation before claiming. For your CT600 filing, Taxpipe guides you through which boxes to complete — though we recommend consulting an R&D specialist for the technical narrative.

Qualifying Expenditure: What Costs Can You Claim?

Only specific categories of expenditure qualify for R&D relief:

1. Staff Costs

• Salaries, wages, and employer's NIC and pension contributions for employees directly involved in R&D
• Must be proportionate to time spent on qualifying R&D activities
• Includes directors' salaries where the director is personally performing R&D

2. Externally Provided Workers (EPWs)

• Agency workers and contractors providing labour for your R&D projects
• Under the merged scheme, claim is limited to the amount paid to the staff provider (or 65% of the payment if through a connected party)

3. Subcontracted R&D

• Costs of R&D subcontracted to third parties
• Under the merged scheme, you can claim on subcontracted R&D at 65% of the cost if the subcontractor is unconnected, or at cost if connected
• Important change from April 2024: Only the company that "controls and directs" the R&D can claim (not the company that merely performs the subcontracted work)

4. Consumable Materials

• Materials used up or transformed in the R&D process
• Electricity, water, fuel, and other utilities directly attributable to R&D
• Prototypes, samples, and test materials (where destroyed or consumed)

5. Software and Data Licences

• Software licence costs where the software is used directly in R&D
• Must be proportionate to R&D use

6. Cloud Computing and Data Costs (New from April 2023)

• Cloud computing costs directly attributable to R&D (e.g., AWS, Azure, GCP)
• Data licence costs directly attributable to R&D
• This was a major expansion — previously, only in-house computing costs qualified

Expenditure That Does NOT Qualify

• Land and property costs
• Capital expenditure (though this may qualify for capital allowances instead)
• Patent costs (separate Patent Box relief may apply)
• Interest and finance costs
• Travel and subsistence (unless directly related to R&D fieldwork)

How to Claim R&D Tax Credits on Your CT600

Step 1: Prepare Your R&D Report

Before touching the CT600, you need a comprehensive R&D report documenting:

• Projects claimed: Description of each R&D project
• Technical uncertainty: What scientific or technological uncertainty was being resolved
• Advance sought: What advance in science or technology the project aimed to achieve
• Resolution: How the uncertainty was (or wasn't) resolved
• Competent professional: Confirmation that the uncertainty wasn't readily deducible
• Expenditure breakdown: Detailed costs allocated to each project by qualifying category

This report isn't filed with the CT600, but HMRC will request it during compliance checks. You must prepare it before claiming.

Step 2: Complete the Additional Information Form (AIF)

From 1 August 2023, all R&D claims must include an Additional Information Form submitted through HMRC's online service before filing the CT600. This form requires:

• Company details and UTR
• Contact details of the person responsible for the claim
• Agent details (if applicable)
• Description of each R&D project (at least one, up to a maximum based on your claim size)
• Qualifying expenditure breakdown by category
• Industry sector (SIC code)

The AIF generates a claim notification number that you'll need for your CT600.

Critical: If you don't submit the AIF before filing your CT600 R&D claim, HMRC will reject the claim.

Step 3: Complete CT600 R&D Boxes

In the main CT600 form:

Step 4: Complete CT600L Supplementary Page

The CT600L is the mandatory supplementary page for R&D claims. It captures detailed information about your claim:

Section A: Merged Scheme Claims

• Total qualifying R&D expenditure
• Enhanced deduction calculation
• Whether claiming above-the-line credit or enhanced deduction

Section B: R&D Intensive Claims

• Whether the company qualifies as R&D intensive
• Calculation of the enhanced credit rate

Section C: Expenditure Breakdown

• Staff costs
• Externally provided workers
• Subcontracted R&D
• Consumable materials
• Software and data licences
• Cloud computing costs

Section D: Additional Information

• Claim notification number (from the AIF)
• Number of R&D projects
• Total qualifying expenditure

For details on all CT600 supplementary pages, see our dedicated guide.

Step 5: Adjust Your Tax Computation

Your iXBRL tax computation must reflect the R&D claim:

1. Include qualifying R&D expenditure in your profit and loss as normal
2. Claim the additional 86% enhanced deduction as a tax adjustment (reducing taxable profits)
3. If loss-making, show the surrender of losses for R&D credit
4. Calculate the corporation tax effect

Filing your CT600 with R&D? Taxpipe supports CT600L supplementary pages and guides you through the R&D boxes. While we handle the filing mechanics, we recommend using an R&D specialist for the technical narrative and expenditure analysis. See our pricing →

Cash Credit vs. Tax Reduction: Which Should You Choose?

If your company is profitable, R&D relief simply reduces your taxable profits (and therefore your corporation tax bill). But if your company is loss-making, you have options:

Option 1: Carry Forward Losses

Keep the enhanced R&D losses and carry them forward to offset against future profits. Choose this if you expect to be profitable soon and want to reduce future tax bills.

Option 2: Surrender Losses for a Cash Credit

Surrender your R&D-enhanced losses to HMRC in exchange for a cash payment. This is valuable for startups and growth companies that need cash now.

Under the merged scheme:

• The credit rate is 16.2% of the surrenderable loss
• For R&D intensive companies, the rate is 27% of the surrenderable loss
• The cash credit is taxable — so the net benefit is slightly less than the headline rate

Example (R&D intensive company):

• Qualifying R&D expenditure: £200,000
• Additional deduction (86%): £172,000
• Total deduction: £372,000
• Company is loss-making — surrenderable loss: £372,000
• Cash credit at 27%: £100,440

This is a significant cash injection for a startup. It's one reason R&D-intensive tech companies should always consider R&D claims.

Option 3: Offset Against Other Tax Liabilities

You can use R&D losses to offset other corporation tax liabilities (e.g., from earlier periods via carry-back).

HMRC Compliance Checks: What to Expect

HMRC has significantly increased R&D compliance activity since 2023. The compliance rate for R&D claims is now estimated at over 20% — meaning 1 in 5 claims faces scrutiny.

Why HMRC Is Scrutinising R&D Claims

• Widespread abuse of the old SME scheme, particularly by aggressive R&D advisory firms
• Claims where the "advance in science or technology" was overstated
• Expenditure incorrectly categorised or inflated
• Missing or inadequate technical narratives

What Happens During a Compliance Check

1. HMRC sends an enquiry letter — usually within 12 months of filing
2. Information request — HMRC asks for your R&D report, technical narrative, expenditure breakdown, contracts, timesheets, and project documentation
3. Technical review — HMRC's R&D specialist reviews whether your projects meet the definition
4. Expenditure review — HMRC checks that costs are correctly categorised and proportioned
5. Outcome — HMRC either accepts the claim, reduces it, or rejects it entirely

How to Protect Your Claim

• Prepare the R&D report before claiming — not after HMRC asks for it
• Be specific about uncertainty — "it was hard" is not enough; explain what was scientifically or technologically uncertain
• Keep contemporaneous records — timesheets, project plans, meeting notes, test results
• Proportionate allocation — don't claim 100% of a developer's time if they also do non-R&D work
• Use a qualified R&D adviser for the technical narrative — this is not a DIY area
• Don't overclaim — conservative, well-documented claims survive scrutiny better than aggressive ones

Remember: Taxpipe helps you file the CT600 and CT600L accurately, but the R&D technical narrative and expenditure analysis should be prepared by an R&D specialist or your technical team. We're a filing tool, not an advisory service.

R&D Tax Credits: Sector-Specific Guidance

Software & Technology Companies

The most common qualifying activities include:

• Developing new algorithms, data structures, or architectures
• Building AI/ML systems with uncertain outcomes
• Creating novel integration approaches between disparate systems
• Performance optimisation beyond current best practice
• Security solutions addressing new or emerging threat vectors

Common mistake: Claiming for routine web development, app building using frameworks, or system administration. These rarely involve scientific or technological uncertainty.

Manufacturing Companies

Qualifying activities often include:

• Developing new manufacturing processes or adapting existing ones
• Working with new materials where properties are uncertain
• Achieving tolerances or specifications beyond standard capability
• Automating processes where the technical approach is unproven

Life Sciences & Pharmaceuticals

Typically includes:

• Drug discovery and development
• Clinical trials
• Medical device development
• Biological process development

Construction & Engineering

May include:

• Novel structural engineering solutions
• Development of new construction methods
• Environmental engineering projects with uncertain outcomes
• Geotechnical challenges requiring innovative approaches

R&D Tax Credits and Other CT600 Reliefs

R&D tax credits interact with several other corporation tax reliefs:

Capital Allowances

If you purchase equipment for R&D, you can claim both:

• Capital allowances on the cost of the equipment itself
• R&D relief on the revenue costs of R&D activities using that equipment

You cannot claim R&D relief on the capital cost of the equipment — only on revenue expenditure.

Patent Box

If your R&D leads to a patent, you can claim Patent Box relief on income from the patented invention (reducing the effective tax rate on that income to 10%). R&D tax credits and Patent Box can be claimed simultaneously on different elements.

Creative Industry Tax Reliefs

If your company is in film, TV, video games, or other creative sectors, separate creative industry reliefs may be more beneficial than R&D credits. You cannot claim both on the same expenditure.

Loss Relief

R&D-enhanced losses can be:

• Carried forward indefinitely
• Carried back 1 year (or 3 years under the terminal loss rules)
• Surrendered for group relief via CT600C supplementary page
• Surrendered for a cash R&D credit

Timeline: How Long Does an R&D Claim Take?

R&D claims must be made within 2 years of the end of the accounting period. Don't wait — file promptly to get your relief or cash credit sooner.

Frequently Asked Questions

Can a small company claim R&D tax credits?

Yes — R&D tax credits are available to companies of all sizes. The merged scheme applies to all companies from April 2024. Small and medium companies that are R&D intensive (R&D spend ≥ 30% of total expenditure) may qualify for the enhanced 27% credit rate.

Do I need to be profitable to claim R&D relief?

No. Loss-making companies can surrender R&D-enhanced losses for a cash credit from HMRC. This is especially valuable for startups that haven't yet reached profitability.

Can I claim R&D tax credits retrospectively?

Yes — you can amend previous CT600 returns to include R&D claims, subject to time limits. The normal amendment window is 12 months from the filing deadline. For older periods, you can make a standalone claim within 2 years of the end of the accounting period.

What is the Additional Information Form (AIF) and when do I need it?

The AIF is a mandatory pre-notification form introduced in August 2023. You must submit it through HMRC's online service before filing a CT600 with an R&D claim. It captures project descriptions, expenditure breakdowns, and contact details. HMRC will reject R&D claims without a valid AIF.

How much can I save with R&D tax credits?

For profitable companies paying 25% corporation tax, the effective saving is 21.5% of qualifying R&D expenditure under the merged scheme. For R&D-intensive loss-making SMEs, the cash credit can be up to 27% of the enhanced loss.

Will HMRC investigate my R&D claim?

Possibly — HMRC's compliance rate for R&D claims is high (estimated 20%+). Claims are more likely to be investigated if they are large relative to company size, from sectors not traditionally associated with R&D, or if the technical narrative is weak. Well-documented claims with genuine uncertainty are unlikely to have problems.

Can I claim R&D tax credits on software development?

Yes — but only if the development involves genuine scientific or technological uncertainty. Building a standard website or app using established frameworks does not qualify. Developing novel algorithms, resolving scaling challenges beyond current best practice, or creating AI systems with uncertain outcomes can qualify.

Do I need an R&D specialist to make a claim?

It's strongly recommended. The technical narrative is the most critical part of your claim, and it requires expertise in both the relevant technology and HMRC's R&D definition. Many companies use specialist R&D advisory firms to prepare the technical narrative and expenditure analysis, then file the CT600 themselves using tools like Taxpipe.

What's the difference between the old SME scheme and the new merged scheme?

The old SME scheme provided a 130% enhanced deduction (or 186% total deduction) and a 14.5% cash credit rate. The merged scheme provides an 86% enhanced deduction and a 16.2% credit rate. However, R&D-intensive SMEs get a 27% credit rate under the new regime, which is more generous than the old scheme for qualifying companies.

Can I claim R&D tax credits on my first CT600?

Yes — there's no waiting period or minimum trading history. New companies can claim R&D relief on their first corporation tax return. In fact, HMRC's advance assurance service is specifically designed for first-time claimants.

Key Takeaways

• R&D tax credits can save 21.5% of your qualifying R&D spend (or generate cash credits of 16.2%–27% for loss-making companies)
• The merged scheme applies from April 2024 — the old SME and RDEC schemes are gone
• You must submit an Additional Information Form (AIF) before filing your CT600 with an R&D claim
• Complete the CT600L supplementary page with your expenditure breakdown
• HMRC compliance is high — prepare a detailed technical narrative before claiming
• Use an R&D specialist for the technical narrative, and a reliable filing tool for the CT600 itself
• Claim within 2 years of the end of your accounting period — don't leave money on the table

Ready to file your CT600 with R&D tax credits? Taxpipe supports CT600L supplementary pages and guides you through every box. Combined with specialist R&D advice for your technical narrative, you'll have a robust, HMRC-compliant claim. Start filing for just £59 →

This guide is for informational purposes only and does not constitute tax advice. R&D tax credit claims are complex and HMRC scrutiny is increasing. We strongly recommend using a qualified R&D tax adviser for your technical narrative and expenditure analysis. Taxpipe is a CT600 filing tool — we help you file your return accurately, but we don't provide R&D advisory services.

Last updated: February 2026

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• R&D Tax Credits for SMEs: Complete Guide to Claiming
• Accounting Periods Explained — When Does Your Corporation Tax Year Start and End?
• HMRC Free Filing Is Ending March 2026 — What You Need to Know