CT600 Box 660: R&D Enhanced Expenditure
CT600 Box 660 records R&D Enhanced Expenditure — the additional deduction that qualifying small and medium-sized companies can claim under the SME R&D Relief scheme on top of their actual research and development costs. If your company meets the SME criteria and has qualifying R&D expenditure in an accounting period beginning before 1 April 2024, Box 660 is where you report this enhanced deduction.
Important: The SME R&D scheme closed to new accounting periods starting on or after 1 April 2024. From that date, most companies — including eligible SMEs — must use the Merged R&D Scheme. If your accounting period began before 1 April 2024, the SME scheme and Box 660 still apply.
What Is R&D Enhanced Expenditure?
When a company carries out qualifying research and development, it can deduct the cost of that R&D from its taxable profits — just as it can with any other allowable business expense. But the UK government created an additional incentive: enhanced expenditure allows you to deduct more than you actually spent.
Under the SME R&D scheme (for accounting periods beginning before 1 April 2024), a company can deduct its actual qualifying R&D costs plus an additional enhancement on top. Box 660 records this additional enhancement amount — not the total expenditure, just the extra amount above your actual costs.
The enhancement rates that have applied under the SME scheme are:
| Period | Additional deduction | Total deduction |
|---|---|---|
| Pre-August 2008 | 50% | 150% |
| August 2008 – March 2011 | 75% | 175% |
| April 2011 – March 2012 | 100% | 200% |
| April 2012 – March 2015 | 125% | 225% |
| April 2015 – March 2023 | 130% | 230% |
| April 2023 – March 2024 | 86% | 186% |
The reduction in the enhancement rate from 130% to 86% from April 2023 was part of a broader reform that increased the RDEC rate and ultimately led to the merged scheme.
Who Qualifies for the SME Scheme?
To use the SME R&D scheme and complete Box 660, your company must meet the SME criteria at the time of the R&D expenditure:
- Fewer than 500 employees
- Annual turnover not exceeding €100 million, or a balance sheet total not exceeding €86 million
Companies that exceed these thresholds are classified as large companies and must use the R&D Expenditure Credit (RDEC) scheme instead. RDEC is reported via CT600 Box 530 rather than Box 660, and works on a fundamentally different mechanism (an above-the-line credit rather than an enhanced deduction).
For a full overview of all R&D tax relief options, see our guide to R&D tax credits for UK companies.
What Counts as Qualifying Expenditure?
Not all R&D costs qualify for the enhanced deduction. Qualifying expenditure under the SME scheme includes:
- Staffing costs — salaries, employer's National Insurance contributions, and pension contributions for employees directly engaged in the R&D activity
- Externally provided workers (EPWs) — agency workers and staff provided by a third party, subject to a 65% cap on the cost
- Software directly used in carrying out the R&D (not general business software)
- Consumable items — materials, power, water, and fuel used and consumed directly in the R&D process
- Payments to clinical trial volunteers
- Subcontracted R&D — payments to subcontractors for R&D work, subject to a 65% cap for connected parties
The R&D must aim to achieve an advance in overall knowledge or capability in a field of science or technology. There must be a genuine scientific or technological uncertainty that competent professionals in the field could not easily resolve — not merely an advance in your company's own knowledge.
What If Your Company Makes a Loss?
If the enhanced deduction creates or increases a trading loss, you have two options:
Option 1: Carry the loss forward Apply the entire loss (including the R&D enhancement) against future trading profits of the same trade. This is straightforward but delays the benefit. See our guide to corporation tax losses for more on loss relief options.
Option 2: Surrender the loss for a payable tax credit A loss-making SME can surrender the portion of its loss attributable to R&D expenditure and receive a cash payment from HMRC. This is known as the "payable R&D credit" and is particularly attractive for early-stage companies that are not yet profitable.
The surrender rates for accounting periods starting on or after 1 April 2023 are:
| Company type | Credit rate |
|---|---|
| Standard | 10% of the surrenderable loss |
| R&D intensive | 14.5% of the surrenderable loss |
Example: A start-up spends £100,000 on qualifying R&D and makes a total trading loss of £200,000. The R&D-related surrenderable loss attributable to the enhanced deduction is £186,000. At 10%, the payable credit = £18,600 receivable from HMRC.
The Additional Information Form
Before making an R&D claim in your CT600, HMRC now requires companies to submit an Additional Information Form (AIF) online through HMRC's portal. The AIF must be submitted before (or at the same time as) the CT600. It captures:
- A description of each R&D project
- The nature of the scientific or technological uncertainty being addressed
- A breakdown of qualifying costs by category (staff, software, consumables, etc.)
- Details of any subcontracted R&D
How to Complete Box 660
To complete Box 660 correctly:
- Identify qualifying expenditure — Calculate the total qualifying R&D costs for the period across all eligible categories
- Apply the enhancement rate — Multiply qualifying expenditure by 86% (for periods starting April 2023–March 2024) or the applicable historic rate from the table above
- Enter in Box 660 — Enter the additional enhanced amount only — not the base qualifying expenditure itself
- Adjust the deductions section — The CT600 deductions section should reflect the total enhanced deduction (actual costs plus the Box 660 enhancement)
- Submit the AIF first — Ensure the Additional Information Form has been filed with HMRC before or alongside the CT600
From April 2024: The Merged R&D Scheme
For accounting periods beginning on or after 1 April 2024, HMRC replaced both the SME scheme and the standalone RDEC scheme with a single Merged R&D Scheme. Under the merged scheme:
- All companies — large and small — claim an above-the-line credit at 20% of qualifying expenditure (verified at GOV.UK)
- The mechanics are RDEC-style (an above-the-line credit, not an enhanced deduction)
- This is reported through different CT600 boxes — Box 660 does not apply to merged scheme claims
- A special Enhanced R&D Intensive Support (ERIS) is available for loss-making companies where at least 30% of total expenditure is qualifying R&D — check current HMRC guidance for the applicable ERIS credit rate
Summary
CT600 Box 660 records the R&D enhanced expenditure under the SME R&D Relief scheme — the additional deduction above your actual qualifying R&D costs. For accounting periods starting after 1 April 2023 but before 1 April 2024, the enhancement is 86% of qualifying expenditure (giving a total 186% deduction). Loss-making companies can surrender R&D-related losses for a payable credit of 10% (or 14.5% if R&D-intensive). From April 2024, the merged R&D scheme replaces the SME scheme, and Box 660 no longer applies to new accounting periods.