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    TaxKilnUK tax guidance
    TaxKilnUK tax guidance

    R&D Tax Credits (Merged Scheme) (Merged R&D)

    TaxKiln framework

    R&D Claim Eligibility Stack

    TaxKiln's stacked eligibility test for the merged R&D scheme (post-April 2024) — qualifying-activity scope + competent-professional standard + technological-advance threshold + ENI test for enhanced rate eligibility.

    Post-April 2024 the merged R&D scheme rewrote the eligibility surface; the TaxKiln R&D Eligibility Stack runs the four tests — qualifying-activity scope, competent-professional standard, technological-advance threshold, and ENI test — in dependency order, because most rejected claims fail at the competent-professional step rather than at the headline activity-scope check.

    From accounting periods beginning on or after 1 April 2024, the UK R&D Tax Credits regime is a SINGLE merged scheme, the old SME enhanced-deduction scheme and the standalone RDEC scheme have been consolidated into one above-the-line 20% credit modelled on RDEC mechanics. The credit applies to all companies regardless of size, with the sole carve-out being R&D-intensive loss-making SMEs who may elect ERIS (Enhanced R&D Intensive Support) instead. Effective net benefit ranges from 14.7p to 16.2p per £1 of qualifying spend depending on Corporation Tax rate position.

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    Guidance, not advice. We explain the rules, we don't assess your situation. Always seek financial or tax advice from your accountant, or contact HMRC. Read our editorial scope →

    What this relief is, in plain English

    R&D Tax Credits reward UK companies for investment in resolving scientific or technological uncertainty. The merged scheme from April 2024 gives a 20% above-the-line credit on qualifying R&D expenditure that flows through your Corporation Tax computation. The credit is treated as deemed taxable trading income and passes through a seven-step relief process. Net benefit depends on your tax position: - Paying main rate CT (25%): 15p per £1 of qualifying spend - Paying Small Profits Rate (19%): 16.2p per £1 - Paying marginal rate (26.5%): 14.7p per £1 - Loss-making (notional 19%): up to 16.2p per £1 as cash credit Loss-making R&D-intensive SMEs (R&D spend ≥30% of total operating costs) can instead elect ERIS, which is more generous, up to 27p per £1 as non-taxable cash credit.

    How it works

    20% above-the-line credit on qualifying expenditure

    Calculate qualifying R&D expenditure (staff costs + subcontractors + EPWs + consumables + software + cloud computing). Apply 20% to get the gross credit. This gross credit is treated as additional taxable trading income on your CT600.

    Seven-step relief process

    Step 1: Set credit against current-period CT liability. Step 2: Apply notional CT charge, 19% (SPR) for loss-makers + small-profit companies; 25% for main rate payers. Step 3: Cap remaining payable element at £20,000 + 300% of PAYE/NIC (more generous than old RDEC formula). Steps 4-7: Sequencing rules for group surrender, carry-forward, and cash payment. Most companies get part of the credit as CT reduction + part as cash payment.

    Subcontractor + EPW rules tightened

    Subcontractor payments + EPWs qualify subject to the historical 65% restriction. Critical April 2024 change: subcontractors + EPWs must now be subject to UK PAYE/NIC. Overseas subcontractors/EPWs restricted to narrow 'wholly unreasonable to replicate' exceptions. Review existing overseas R&D arrangements urgently, these may no longer qualify under the merged scheme.

    Additional Information Form required pre-filing

    Since 8 August 2023, the Additional Information Form (AIF) must be submitted BEFORE the CT600 containing the R&D claim. The AIF includes company details, R&D activities description, scientific/technological uncertainty being addressed, breakdown of costs, and named senior R&D officer (typically a director with technical credibility, not just the accountant).

    Who qualifies

    Interactions with other reliefs

    ERIS (Enhanced R&D Intensive Support)

    ERIS is the carve-out for loss-making R&D-intensive SMEs (R&D spend ≥30% of total operating costs). If eligible, ERIS gives up to 27p per £1 as non-taxable cash credit, more generous than the merged scheme's 16.2p loss-maker rate. Election is made on the CT600.

    Patent Box

    Patent Box (10% effective CT rate on profits from patented inventions) can apply ALONGSIDE R&D Tax Credits on the same project, different relief mechanisms on different aspects. R&D credit on input costs + Patent Box on output profits. Sequence: claim R&D credit first, then apply Patent Box to the post-R&D profits attributable to patented inventions.

    Annual Investment Allowance (AIA)

    AIA on plant + machinery purchased for use in R&D projects can be claimed alongside R&D Tax Credits on the staff cost of using that plant. Different reliefs attaching to different aspects of the same project, AIA on the asset, R&D credit on the operational R&D work.

    Subsidised R&D

    Major change under merged scheme: subsidised + grant-funded R&D is FULLY ELIGIBLE for credit (previously SME scheme blocked or restricted such relief). Companies that previously could not claim SME relief on grant-funded R&D may find that same expenditure is now fully eligible, significant change worth reviewing for R&D projects with mixed funding.

    Common mistakes + audit triggers

    Worked example

    Marek, Cardiff - sole-director Ltd Co software development consultancy with bespoke ML platform R&D (2025/26)

    Year ending 31 March 2026 (first full merged-scheme accounting period). Total UK qualifying R&D expenditure £180,000 (1 director's R&D time + 1 R&D contractor on UK PAYE + cloud computing on AWS + ML training data licences). Total company profit before R&D credit: £140,000.

    Calculation: **Step 1: Calculate above-the-line credit.** 20% × £180,000 qualifying spend = £36,000 gross credit. **Step 2: Notional CT charge.** Company is in marginal relief band (£50k SPR upper – £250k main rate lower). Notional charge at 25% main rate × £36,000 = £9,000 notional CT. **Net above-the-line credit value: £36,000 - £9,000 = £27,000 cash benefit.** **Step 3: Set against current-period CT liability.** Profit £140,000 with marginal relief; effective CT (before credit) ~£28,000. R&D credit £27,000 reduces CT to approximately £1,000 net. **Step 4: PAYE cap check.** Company PAYE/NIC for the period: £15,000. Cap = £20,000 + (300% × £15,000) = £65,000. Cap not breached. **Effective net benefit:** £27,000 (15p per £1 of qualifying spend at marginal rate). Without R&D Tax Credits, Marek would have paid the full ~£28,000 CT. With the credit, CT reduces to ~£1,000. **Additional Information Form filed:** before the CT600 submission. R&D activity: development of bespoke ML training pipeline for time-series anomaly detection, meets BEIS definition (advance in machine learning technique; uncertainty around whether the approach can achieve required accuracy with available training data). Named senior R&D officer: Marek (director with technical credibility, Computer Science degree + 8 years ML engineering experience).

    Statute reference: Corporation Tax Act 2009 + Finance Act 2024 Part 6A (as amended). HMRC manual: CIRD80000.

    Frequently asked questions

    What happens if I miss the Self Assessment deadline?+
    The Self Assessment deadline is 31 January (online filing) for the previous tax year. Miss it and HMRC apply an automatic £100 penalty. Beyond that: £10 per day from 3 months late (capped at £900), 5% of tax due at 6 months late, and another 5% at 12 months late, under Schedule 55 of the Taxes Management Act 1970. If you have a genuine reason (serious illness, bereavement, technical issue with HMRC's systems) you can appeal with evidence; HMRC accepts reasonable excuse appeals in most genuine cases.
    Do I need an accountant or can I file Self Assessment myself?+
    Legally you can file Self Assessment yourself via gov.uk for free, most simple sole-trader returns (single income source, basic expenses) are realistic to self-file. An accountant adds real value when: your trading profit is above £40,000 (extraction-strategy decisions matter), you have multiple income streams (PAYE + self-employment + property + dividends), you've crossed the £90,000 VAT threshold, you're considering incorporation, or you have an HMRC enquiry. Expect to pay £400-£1,500/year for a typical sole-trader accountant; the cost is itself a deductible expense.
    How do payments on account work?+
    When your Self Assessment tax bill exceeds £1,000 for the first time, HMRC requires payments on account toward NEXT year's tax. Half the current bill is due 31 January (alongside the current bill); the other half is due 31 July. So your first January after crossing the threshold can hit with a double-bill: last year's balance + first payment on account. Adjust via Form SA303 if you expect next year's income to drop substantially. Payments on account don't apply if more than 80% of your tax is collected via PAYE.
    My accounting period straddles 1 April 2024, which scheme applies?+
    Standard 12-month periods: a 31 March year-end company files under the OLD scheme for the period ending 31 March 2024 + under the merged scheme for the period beginning 1 April 2024. No straddling. A 31 December year-end company experienced its first merged-scheme accounting period beginning 1 January 2025 (year ending 31 December 2025). Non-standard 'longer period of account' straddling 1 April 2024 (e.g. 18-month periods, change of accounting date) is split into two corporation tax accounting periods at 31 March 2024, first under old rules, second under merged.
    Can subcontractor + EPW costs still be claimed under the merged scheme?+
    Yes, but with restrictions. Subcontractor payments + Externally Provided Workers (EPWs) qualify subject to the historical 65% restriction (only 65% of payments to unconnected parties are eligible). Critical change: from April 2024, subcontractors + EPWs must be subject to UK PAYE/NIC. Overseas subcontractors/EPWs are now restricted to a narrow 'wholly unreasonable to replicate' exception (e.g. clinical trials needing patients in tropical climates). This is a significant tightening from the pre-April-2024 rules where overseas was broadly allowed.
    What's the difference between Merged Scheme and ERIS?+
    ERIS (Enhanced R&D Intensive Support) is a carve-out FROM the merged scheme for the most R&D-intensive loss-making SMEs. ERIS broadly preserves the generous economics of the pre-2024 SME scheme. Eligibility: loss-making SME + R&D spend ≥30% of total operating costs in the period. Under ERIS, payable credit is up to 27% of qualifying spend (vs 16.2p per £1 under loss-making Merged Scheme). The payable ERIS credit is NOT itself taxable (unlike the merged RDEC credit). Most loss-making SMEs are better off in ERIS if they qualify.
    Do I need to file an additional information form before claiming R&D?+
    Yes, since 8 August 2023, claims require submission of an Additional Information Form (AIF) BEFORE filing the CT600. The AIF includes: company details, R&D contact, R&D activity description, scientific/technological uncertainty being resolved, breakdown of qualifying costs, named senior R&D officer. Claims without the AIF are invalid + will be rejected. Many advisors recommend the senior R&D officer being a director with technical credibility, HMRC has rejected claims signed off by accountants with no technical R&D understanding.

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