The CT600 carries the flags and the totals; the CT600L does the arithmetic. Tick box 656 to confirm the claim notification and box 657 the Additional Information Form, work the credit down the CT600L, then copy three figures back: L210 to box 530, L125 to box 880, L180 to box 875. Which part of the CT600L you use turns on the scheme: the merged credit runs through the same boxes whatever the size of the claimant.
Sequence first — it is the easiest way to lose a claim that is otherwise sound. The Additional Information Form has to reach HMRC before or on the same day as the return; the boxes confirm that the form and the notification were submitted, and ticking them does not submit anything. Box 650 flags an SME claimant, box 655 a large company — the company, not the scheme, so an SME on the merged credit ticks 650. How to claim R&D tax credits sets the order out.
Which section of the CT600L does each scheme use?
The boxes were laid out for the old two-scheme world and the labels still show it: L5 to L165 is expenditure credit. Boxes L166 to L190 sit under a heading naming both — “Small and medium-sized enterprise (SME) R&D and enhanced support for R&D intensive SME (ERIS)” — but for a period beginning on or after 1 April 2024 the SME half is dead, and the legacy boxes L185 and L190 with it. Only a company qualifying for enhanced R&D intensive support belongs there; an SME on the merged credit stays out.
Claim the merged scheme and ERIS for the same period and the two sections talk to each other twice. The PAYE and National Insurance figures go in once, at L167 to L169A, and L71 to L73A stay blank. The two claims share one cap instead of getting one each: L75 becomes three times the sum of L168 and L169, plus £20,000, less the ERIS credit at L170. The PAYE cap on R&D tax credits works that arithmetic through.
How do the seven payment steps run down the form?
Show the gross credit as taxable income before the steps run, in the accounts or the computations. Qualifying expenditure goes in at L10, the gross credit at L15. Ahead of step 1 sits a pre-step: a notional tax restriction brought forward, or a credit surrendered by a group member, goes in at L5 and discharges this period’s corporation tax at L7.
Step 1 discharges the corporation tax liability for the period itself. L30 carries it in — from L9 where the pre-step ran, otherwise from box 475 — L35 removes the income tax at box 515 set against it, leaving the maximum set-off at L40, and L45 is the lower of that and the total credit at L25.
Step 2 is the notional tax deduction, at L50 to L65. It reduces the payable element by notional tax: at the 25% main rate where the company has profits chargeable at that rate, and at the 19% small profits rate in any other case, a loss-maker included. That is the difference between 15p and 16.2p of net credit per £1 of qualifying spend. The restricted amount is carried forward at L65, not lost.
Step 3 is the PAYE and National Insurance cap, at L70 to L80. L71 is the exception: a company creating or managing its own intellectual property, with connected-party externally provided worker and subcontractor spend within 15% of qualifying expenditure, is outside the cap, and L71A must be completed with it. Otherwise L75, for a period beginning on or after 1 April 2024, is £20,000 plus 300% of relevant PAYE and National Insurance liabilities — less any ERIS credit where both schemes are claimed — the £20,000 proportionately reduced for a short period. What exceeds the cap drops out at L80, reaches the next period through L145, and comes back at L20 on next year’s form.
Steps 4 to 6 discharge corporation tax for other periods at L90, surrender to a group member at L100, and settle anything else owed to HMRC — L110 for liabilities on this return, L115 for those outside corporation tax, such as PAYE or VAT.
Step 7 is the remainder. L15 is completed gross, including any amount the going concern rules hold back; it comes out again at L123, where a current-period claim records what is not payable because the company was not a going concern. L125 is the payable credit; the condition is on who can claim R&D tax relief.
How do a payable amount, an offset and a group surrender each appear?
Paid out. L125 goes to box 880, with X in box 40 and the bank details at boxes 920 to 940, which HMRC asks for to avoid delays.
Set against tax. Four boxes collect it: L194 for the pre-step discharge, L195 for step 1, L200 for step 6, L205 for an ERIS credit. Their total at L210 goes to box 530, which covers only liabilities on this return: L90 and the L115 half of step 6 both stay outside it.
Surrendered to a group member. The step 5 amount goes in at L100 and again at L160; the step 2 restriction can be surrendered too, at L135 and L155, totalled at L165. No box names the recipient, so the computations must. The receiving company shows the credit at box 615 of its own return and may bring it in at L5, even with no R&D claim of its own — though not for a surrender made after its amendment window has closed. R&D tax relief in groups covers who claims what.
What does an ERIS claim look like on the return?
The CT600L only comes in where a payable credit is claimed: an ERIS claim taken as the additional deduction alone stops at box 660. Box 653 adds that the SME is R&D intensive, and can only be ticked where 650 is. Box 659 takes the qualifying expenditure, box 660 the enhanced expenditure — that figure plus the 86% additional deduction.
On the CT600L, L166 repeats box 659 and must agree with it. L170 is the credit claimed: 14.5% of the surrenderable loss, subject to the cap. L175 is the part set against other liabilities on the return, and L180, the balance, goes to box 875 — “Payable Research and Development tax credit” on the form. Two traps. Merged-scheme expenditure goes in neither box 659 nor box 660 — both boxes say so — so it appears at L10 and nowhere else. And the loss surrendered for the credit is written off in the computations: it must not reappear in the losses carried forward.
If the numbers do not tie across the return, computations and form, talk it through with us.
Sources
- Completing the CT600L page for research and development — every box cited above, last updated 6 April 2026: the pre-step 1 boxes L5 to L9, the seven steps at L10 to L125, the carry-forward and surrender boxes L129 to L165, the intensive-support section L166 to L190 (for periods beginning on or after 1 April 2024, completed only where the company qualifies for ERIS), the set-off total L194 to L210, the instruction to leave L71 to L73A blank where both schemes are claimed, the two forms of the L75 cap — £20,000 plus 300% of relevant PAYE and NIC where only the expenditure credit is claimed, and that figure reduced by the L170 credit where both schemes are claimed — with the £20,000 proportionately reduced for a short period, the L71 exception and the L71A entry it obliges, the gross entry at L15 with going-concern amounts removed at L123, and the requirement that the computations name the group company a credit is surrendered to.
- Completing your Company Tax Return (CT600 guide) — last updated 2 June 2026: box 475 net corporation tax liability, box 515 income tax deducted, box 530 (from L210), box 615 credits surrendered to this company, boxes 650, 653, 655, 656 and 657, boxes 659 and 660 (both of which exclude expenditure qualifying for the expenditure credit), box 875 (from L180), box 880 (from L125), box 40 and the bank details at boxes 920 to 940, and the four conditions for box 943.
- Make a claim for R&D tax relief on your company tax return — the credit shown as taxable income in the profit and loss account or added to profit in the computations, the tick boxes, the seven steps in plain terms, and the CT600L requirement for each scheme — for ERIS, only “if you’re claiming a payable tax credit”, which the CT600L’s own “when to complete” section matches.
- CT600L supplementary page — the form itself, last updated 6 April 2026, carrying the printed heading over L166 to L190: “Small and medium-sized enterprise (SME) R&D and enhanced support for R&D intensive SME (ERIS)”.
- CTA 2009 s1042I — the seven steps the form follows, with s1042J adding any amount deducted at step 3 to the credit for the next accounting period even where that amount would otherwise be nil, s1042K the notional tax deduction at step 2, s1042L allowing that deducted amount to be surrendered to a group member or carried forward against a later period’s corporation tax, and s1042N the mechanics of a surrender.
- CTA 2009 s1112B — the cap of £20,000 plus three times the company’s relevant PAYE and NIC liabilities, proportionately reduced where the accounting period is less than twelve months; subsection (4) reduces the merged-scheme cap by any R&D tax credit obtained under Chapter 2, so a company claiming both schemes gets one cap and not two. s1112E is the exception flagged at L71: a company creating or managing its own relevant intellectual property, whose connected-party externally provided worker and subcontractor expenditure is within 15% of qualifying expenditure, has no cap at all.
- CTA 2009 s1112F — nothing is paid at step 7 where the company was not a going concern when it claimed; s1112H — payment is not required while the return is under enquiry, or where PAYE and NIC liabilities are outstanding.
- CTA 2009 s1055, s1058 and s1062 — the surrenderable loss capped at 186% of qualifying expenditure, the credit at 14.5% of it subject to the same PAYE and NIC cap, and the reduction of the loss carried forward by the amount surrendered.
- CIRD112100: the payment steps under the merged scheme — HMRC’s own walk-through, including that the steps run even where there is no new claim but an amount was carried forward from step 3.
- CIRD122000: ERIS calculation — the 86% additional deduction, the 14.5% credit, and the surrender effected by writing the losses off in the company’s tax computations.
- CIRD81805: restriction of nominations and assignments — for claims made on or after 1 April 2024 HMRC generally pays only the claimant company, which supplies its own payment details on the CT600.
This page describes the rules as they stood at the review date above, as general information rather than advice on your circumstances. For how that distinction works, see our terms; for an answer on your own facts, talk to us.