Supplementary pages CT600L: research and development
Source: gov.uk (2025-07-24)

How to complete supplementary pages CT600L and what information you need to include.

When to complete

Complete these supplementary pages if your company is claiming both or one of the following:
- research and development (R&D) expenditure credit (RDEC)
- R&D payable tax credit for small and medium sized enterprises (SME)
For more information, read:
- the Corporate Intangibles Research and Development Manual CIRD80000: Research and development tax relief (https://www.gov.uk/hmrc-internal-manuals/corporate-intangibles-research-and-development-manual/cird80000)
- chapter 6A of Part 3 of the Corporation Tax Act 2009 (https://www.legislation.gov.uk/ukpga/2009/4/part/3/chapter/6A) (R&D expenditure credit)
- part 13 of the Corporation Tax Act 2009 (https://www.legislation.gov.uk/ukpga/2009/4/part/13#:~:text=(1)This%20Part%20provides%20for,section%2087%20for%20the%20expenditure) (R&D relief for small and medium sized enterprises)
For accounting periods starting on or after 1 April 2024, the merged scheme RDEC and enhanced R&D intensive support (ERIS) will replace the old RDEC and SME schemes.

Read more information about R&D tax relief — the merged scheme and enhanced R&D intensive support (https://www.gov.uk/guidance/research-and-development-rd-tax-relief-the-merged-scheme-and-enhanced-rd-intensive-support).

Company information

L1 Company name

Enter the company name.

L2 Tax reference

Enter the company’s 10-digit Unique Taxpayer Reference.

Period covered by this supplementary page (cannot exceed 12 months)

L3

Enter the start date using the format DD MM YYYY.

L4

Enter the end date of the accounting period using the format DD MM YYYY.

Pre-step 1 restriction

Complete this section if you either:
- have an amount of step 2 restriction brought forward from a previous accounting period
- wish to include an amount of RDEC surrendered from other group companies
L5 Step 2 restrictions brought forward from previous accounting periods or surrendered from group companies, or both

Enter the total amount of step 2 restrictions which have been brought forward from previous accounting periods.

You can include any step 2 or step 5 RDEC surrendered from other group companies, which can be used by the company for this accounting period (read section 104O (https://www.legislation.gov.uk/ukpga/2009/4/section/104O) and section 104R (https://www.legislation.gov.uk/ukpga/2009/4/section/104R) of the Corporation Tax Act 2009). You may do this even if you are not claiming for RDEC or SME payable tax credit yourself in this return.

If you include a surrendered amount, make sure the surrendering group company includes the details in their computations so HMRC can account for the credit. You can discharge Corporation Tax liability in preference to any section 104N(2) of the Corporation Tax Act 2009 (https://www.legislation.gov.uk/ukpga/2009/4/section/104N) carried forward RDEC. To do so, enter a figure reflecting the company’s use of either:
- step 2 of section 104N(2) of the Corporation Tax Act 2009
- step 5 surrendered RDEC
You do not have to include RDEC surrendered to your company under steps 2 or 5 from another group company in your CT600L — but you can choose to do so. If you do, make sure the surrender was not made after the time in which the recipient can submit an amendment.

If any surrendered step 2 or 5 amounts are not included in the CT600L, the details of the surrendering group company must be included in your computations.

L6 Corporation Tax liability

Enter the figure from box 475 of your CT600 form.

L7 Amount of step 2 brought forward and surrendered RDEC used to discharge Corporation Tax liability

Enter the lesser figure of boxes L5 and L6. Copy this figure to box L194.

L8 Amount of step 2 brought forward RDEC carried forward to next accounting period

Enter the figure in box L5 minus the figure in box L7. Copy this figure to box L129.

L9 Remaining Corporation Tax liability carried forward to step 1.

Enter the figure in box L6 minus the figure in box L7.

Step 1: calculation of RDEC set against Corporation Tax liability

Read the Corporate Intangibles Research and Development Manual CIRD89780: R&D expenditure credit (RDEC) scheme: payment of credit Chapter 6A CTA 2009 S104N and 104O (https://www.gov.uk/hmrc-internal-manuals/corporate-intangibles-research-and-development-manual/cird89780) for more information.

L10 R&D expenditure on which RDEC is claimed in this accounting period

Enter the amount of expenditure which qualifies for RDEC during this accounting period and on which RDEC is claimed.

L15 RDEC claim for this accounting period

Enter the amount of the total RDEC claimed before any discharges or surrenders for example. Include any amounts which are extinguished by the going concern rules at this stage (read section 104S(2)(b) of the Corporation Tax Act 2009 (https://www.legislation.gov.uk/ukpga/2009/4/section/104S)). Those amounts are removed in box L123.

L20 Step 3 amounts from a previous accounting period treated as RDEC for this accounting period

Enter the total amount of section 104N(2) (https://www.legislation.gov.uk/ukpga/2009/4/section/104N) step 3 which has been carried forward from earlier periods.

L25 Total RDEC for the accounting period

Enter the sum of boxes L15 and L20.

L30 Remaining Corporation Tax liability

Enter the figure from box L9. If you did not complete box L9, enter the figure from box 475 of your CT600 form.

L35 Income Tax deducted from profits (applicable to Corporation Tax liability)

Enter the element of Income Tax deducted from gross profits and shown in box 515 which needs to be set against the Corporation Tax liability at box 475. This will be the full amount if there is no other liability in boxes 480 to 505.

If there are other liabilities in boxes 480 to 505, a fair and reasonable apportionment can be made between those liabilities and the box 475 liability. Only the liability which is apportioned against box 475 should be entered in box L35.

L40 Maximum amount available for step 1 set off

Enter the figure in box L30 minus the figure in box L35.

L45 Amount of RDEC used to discharge Corporation Tax at step 1

Enter the lesser figure of boxes L25 and L40. If box L40 is not completed then enter 0.00. Copy the figure from box L45 to box L195.

Step 2: calculation of notional tax charge

Only complete step 2 if you have RDEC remaining after completing step 1.

This step restricts the potential payable element and makes sure that loss makers receive the same net benefit as profit makers (the credit being taxable). This is achieved by retaining a notional tax so the total cash benefit for all claimants is equal to the expenditure credit, net of tax at the main rate of Corporation Tax.

L50 Step 1 balance carried forward to step 2

Enter the figure in box L25 minus the figure in box L45.

L55 Corporation Tax charge on RDEC for this accounting period

Enter the figure in box L15 multiplied by the tax rate for this accounting period.

L60 Total RDEC arising in this accounting period (AP) less Corporation Tax charge on the RDEC for this AP

Enter the figure in box L15 minus the figure in box L55.

L62 RDEC arising in this AP less remaining Corporation Tax liability at step 1

Enter the figure in box L15 minus the figure in box L40. If box L40 exceeds box L15 enter 0.00.

L65 Step 2 restriction carried forward to next accounting period

Enter the figure in box L62 minus the figure in box L60. If box L60 exceeds box L62 enter 0.00.

Step 3: PAYE and National Insurance Contributions liability cap

Only complete step 3 if you have RDEC remaining after completing step 2.

This step further restricts any payable element to the company’s total expenditure on R&D workers’ PAYE and National Insurance contributions for the accounting period. The calculation of the capped credit for R&D workers’ PAYE and National Insurance contributions is set out in the Corporate Intangibles Research and Development Manual. Read about:
- the restriction of total expenditure on R&D workers’ PAYE and NIC (https://www.gov.uk/hmrc-internal-manuals/corporate-intangibles-research-and-development-manual/cird89790)
- the total amount of company’s PAYE and NIC liabilities (https://www.gov.uk/hmrc-internal-manuals/corporate-intangibles-research-and-development-manual/cird89800)
L70 Step 2 balance carried forward to step 3

Enter the figure in box L50 minus the figure in box L65.

L75 PAYE and National Insurance contribution liability cap

For accounting periods starting before 1 April 2024, enter the amount of total relevant expenditure on R&D workers’ PAYE and National Insurance contributions.

For accounting periods starting on or after 1 April 2024, if the exemption from the PAYE cap at s1112E CTA 2009 (https://www.legislation.gov.uk/ukpga/2009/4/section/1112E) does not apply and the company is claiming:
- RDEC only — enter £20,000 plus 300% of the company’s relevant PAYE and National Insurance contributions liabilities
- under both the RDEC and ERIS schemes — the amount in this box is £20,000 plus 300% of the company’s relevant PAYE and National Insurance contributions liabilities, reduced by the ERIS payable credit figure entered in box L170
In either case if the accounting period is less than 12 months, the £20,000 is proportionately reduced.

Find out more about the PAYE cap (https://www.gov.uk/guidance/research-and-development-rd-tax-relief-the-merged-scheme-and-enhanced-rd-intensive-support).

If the exemption from the PAYE cap does apply, make sure that the amount entered in this box equals the amount entered in box L70.

L80 Step 3 restriction carried forward to next AP

Enter the figure in box L70 minus the figure in box L75. If box L75 exceeds box L70 enter 0.00. Copy the figure from box L80 to box L145.

Step 4: RDEC to be offset against outstanding Corporation Tax liabilities

Any amount remaining after step 3 is used to discharge any outstanding Corporation Tax liabilities (due but not settled) of the company for any other accounting periods.

L85 Step 3 balance carried forward to step 4

Enter the figure in box L70 minus the figure in box L80.

L90 Amount used to discharge Corporation Tax liability of another accounting period

The figure cannot exceed the figure in box L85.

Step 5: amount surrendered to group member

If the company is a member of a group it may surrender the whole, or any part remaining after step 4, to any other group member. Read CIRD89810: surrender of credit to another group company (https://www.gov.uk/hmrc-internal-manuals/corporate-intangibles-research-and-development-manual/cird89810) for more information.

L95 Step 4 balance carried forward to step 5

Enter the figure in box L85 minus the figure in box L90.

L100 Credit surrendered to group member

The figure cannot exceed the figure in box L95. Copy the figure from box L100 to box L160. Your computations must include details of the other group member you are surrendering the credit to.

Step 6: amount used to discharge other company liabilities

Any amount remaining after step 5 is used to discharge any other liability of the company to pay a sum to the Commissioners, for example VAT or liabilities under any contract settlement.

L105 Step 5 balance carried forward to step 6

Enter the figure in box L95 minus the figure in box L100.

L110 Amount used to settle other company liability on this Corporation Tax Self Assessment

Enter amount used to discharge liability on the return, including those which are not Corporation Tax but treated as such. For example, Bank Levy, controlled foreign company tax, tax on loans to participators. Copy the figure from box L110 to box L200.

L115 Amount used to discharge any other company liability

Enter amount used to discharge other liability outside Corporation Tax. For example, PAYE or VAT. The figure cannot exceed box L105 minus box L110.

L120 Total used to discharge other company liability

Enter the sum of boxes L110 and L115.

Step 7: payable Research and Development expenditure credit

The final amount remaining is payable to the company provided that the company is a going concern. Read the Corporate Intangibles Research and Development Manual CIRD81130: company a going concern (SME and vaccines schemes only) (https://www.gov.uk/hmrc-internal-manuals/corporate-intangibles-research-and-development-manual/cird81130) for more information.

L123 Amounts extinguished by s104S (2)(b) CTA 2009

Enter the whole amount extinguished by section 104S of the Corporation Tax Act 2009 (https://www.legislation.gov.uk/ukpga/2009/4/section/104S) (the going concern rules).

L125 Payable RDEC

Enter the figure in box L105 minus the sum of boxes L120 and L123.

Enter the figure from box L125 into box 880 of your CT600 form.

RDEC carried forward

L129 Pre-step 1 restriction

Enter the figure from box L8. This figure can only include unused step 2 amounts carried forward. It cannot include any surplus step 2 surrender from group companies amounts.

L130 Step 2 restriction

Enter the figure from box L65.

L135 Surrendered to other group company

Copy the figure from box L135 to box L155. Your computations must include details of the other group company you are surrendering the credit to.

L140 Balance carried forward to next AP

Enter the sum of boxes L129 and L130 minus box L135.

L145 Step 3 restriction

Enter the figure in box L80.

L150 Total carried forward to next AP

Enter the sum of box L140 and box L145.

RDEC surrendered

L155 Step 2 restriction surrendered

Enter the figure in box L135.

L160 Step 5 Credit surrendered to group member

Enter the figure in box L100.

L165 Total surrendered

Enter the sum of box L155 and box L160.

Small and medium-sized enterprise (SME) R&D and enhanced support for R&D intensive SMEs

For information on SME relief, read:
- the Corporate Intangibles Research and Development Manual CIRD90000: SME scheme (https://www.gov.uk/hmrc-internal-manuals/corporate-intangibles-research-and-development-manual/cird90000)
- section 1039 of the Corporation Tax Act 2009 (https://www.legislation.gov.uk/ukpga/2009/4/section/1039)
For accounting periods starting on or after 1 April 2024, this section must only be completed if you qualify under the enhanced R&D intensive support.

For information on ERIS, read the Corporate Intangibles Research and Development Manual CIRD120000: ERIS (https://www.gov.uk/hmrc-internal-manuals/corporate-intangibles-research-and-development-manual/cird120000).

L166 R&D expenditure

Enter the amount of R&D Expenditure which qualifies for relief within the SME R&D scheme for this accounting period and on which SME R&D Relief is claimed. The figure in this box must match the entry in box 659 of your CT600 form.

L167 Does the exception at s1058D CTA 2009 apply?

Enter ‘X’ if the exception at section 1058D of the Corporation Tax Act 2009 (https://www.legislation.gov.uk/ukpga/2009/4/section/1058D) applies.

L167A Total expenditure on externally provided workers from, and subcontracting to, connected persons

Enter a figure that is equal to, or less than, the figure in box L166 multiplied by 15%. This box must be completed if exception at section 1058D (https://www.legislation.gov.uk/ukpga/2009/4/section/1058D).

L168 PAYE/NIC for which the company is liable in this accounting period

Enter the amount of PAYE and National Insurance contributions that your company is liable for in this accounting period.

L168A Employer PAYE reference

Enter your employer PAYE reference number.

L169 Relevant PAYE/NIC liability of connected companies

Enter the amount of PAYE and National Insurance contribution liabilities of any connected companies.

L169A Connected companies’ employer PAYE reference

Enter the employer PAYE reference numbers of any connected companies.

Small and medium sized enterprise (SME) R&D

L170 SME/R&D intensive SME R&D payable tax credit claim for this accounting period

Section 1058D of the Corporation Tax Act 2009 (https://www.legislation.gov.uk/ukpga/2009/4/section/1058D) (and, for accounting periods beginning on or after 1 April 2024, section 1112E (https://www.legislation.gov.uk/ukpga/2009/4/section/1112E)) identifies exceptions to the tax credit cap. If these exceptions do not apply, the figure you enter in this box must not exceed the sum of boxes L168 and L169 multiplied by 3 plus £20,000.

For more information about SME relief:
- read R&D tax relief: SME scheme: payable tax credit — for surrenderable loss (https://www.gov.uk/hmrc-internal-manuals/corporate-intangibles-research-and-development-manual/cird90500)
- read R&D Tax Reliefs: reformed reliefs: ERIS calculation (https://www.gov.uk/hmrc-internal-manuals/corporate-intangibles-research-and-development-manual/cird122000)
L175 SME/R&D intensive SME R&D payable tax credit set off against other liabilities on this return

Enter the amount of credit that is being set off against other liabilities on this return including those in boxes 480 to 505 of your CT600 form. The figure cannot exceed the figure in box L170. Copy the figure from box L175 to box L205.

L180 SME/R&D intensive SME balance payable tax credit

Enter the figure in box L170 minus the figure in box L175.

Enter the figure from box L180 into box 875 of your CT600 form.

L185 SME RDEC claim from work subcontracted to it by a large company

Enter the total RDEC claimed under sections 104C to 104E of the Corporation Tax Act 2009 (https://www.legislation.gov.uk/ukpga/2009/4/part/3/chapter/6A/crossheading/smes-qualifying-expenditure-on-subcontracted-rd).

For more information, read the Corporate Intangibles Research and Development Manual:
- to find out about claims by SME (https://www.gov.uk/hmrc-internal-manuals/corporate-intangibles-research-and-development-manual/cird89740)
- to find information about R&D contracted to a SME (https://www.gov.uk/hmrc-internal-manuals/corporate-intangibles-research-and-development-manual/cird89750)
L190 SME RDEC claim from subsidised and capped work

Enter the total RDEC claimed under section 104F (https://www.legislation.gov.uk/ukpga/2009/4/part/3/chapter/6A/crossheading/smes-subsidised-qualifying-expenditure) to section 104I (https://www.legislation.gov.uk/ukpga/2009/4/part/3/chapter/6A/crossheading/smes-capped-rd-expenditure) of the Corporation Tax Act 2009.

For more information, read the Corporate Intangibles Research and Development Manual:
- to find out about claims by SME (https://www.gov.uk/hmrc-internal-manuals/corporate-intangibles-research-and-development-manual/cird89740)
- to find information about subsidised qualifying expenditure (https://www.gov.uk/hmrc-internal-manuals/corporate-intangibles-research-and-development-manual/cird89760)
Total R&D set off against liabilities in this Company Tax Return

L194 RDEC pre-step 1 discharge amount

Enter the figure from box L7.

L195 RDEC step 1 discharge amount

Enter the figure from box L45.

L200 RDEC step 6 discharge amount for this accounting period

Enter the figure from box L110.

L205 SME R&D payable tax credit used to discharge other liabilities on this return

Enter the figure from box L175.

L210 Total

Enter the sum of boxes L194, L195, L200 and L205.

Enter the figure from box L210 into box 530 of your CT600 form.