What goes in each box of the CT600?

Which boxes identify the company and the return period?

Boxes 1 to 4 identify the company and boxes 30 and 35 give the start and end dates of the period the return covers.

An accounting period for Corporation Tax cannot be longer than 12 months, so accounts covering a longer period need two returns. The tick boxes that follow the period are covered in the next section.

Source: HMRC Company Tax Return guide — Company details and period · GOV.UK: Accounting periods for Corporation Tax | Guides: What is a UTR and where do I find it? · First company accounts: why you may need two CT600s

Which "About this return" boxes might you need to tick?

Boxes 40 to 75 are tick boxes: put an X in each one whose statement applies to the company for the period, such as a repayment due (box 40) or estimated figures (box 55), and leave the rest blank. None of them holds an amount.

For transfer pricing, HMRC says small and medium-sized enterprises do not normally have to apply the rules: here that means a group employing fewer than 250 people worldwide with a global turnover under 50 million euros (£34 million), a balance sheet total under 43 million euros (£29 million), or both. After box 75, the form asks whether you are attaching accounts and computations for the period, and HMRC says you must include computations that show how the figures in the return were calculated from the company's accounts. Some filing software, Taxley included, shows the choice between a new and an amended return as box 38; it is not a box on the form.

Source: HMRC Company Tax Return guide — About this return · HMRC manual CTM93280: estimated figures in returns · HMRC manual EM1513: qualifying conditions to be a small group | Guide: CT600 tick boxes 38 to 75: when to tick each one in 2026

Which boxes cover turnover and trading profits?

Box 145 is the company's trading turnover and box 155 its taxable trading profit; box 160 takes off trading losses brought forward, leaving net trading profits in box 165.

Source: HMRC Company Tax Return guide — Turnover and trading profits | Guide: Accounting profit vs taxable profit: a CT600 example

Which boxes cover interest and non-trading loan relationships?

Box 170 holds the net profit on the company's non-trading loan relationships, such as bank interest received; a net deficit goes in box 795, and boxes 260 and 263 set this period's and earlier periods' deficits against total profits.

Interest and other loan relationship credits and debits of a trade are not entered here: HMRC says they are brought into account in working out the trading profit.

Source: HMRC Company Tax Return guide — Interest and loan relationships

Which boxes cover property income?

Box 190 is the profit of the company's property business; a UK property business loss arising in the period goes in box 805, and property losses set against total profits go in box 250.

Source: HMRC Company Tax Return guide — Property income and losses | Guide: Corporation Tax for a property (rental) company

Which boxes cover chargeable gains and other income?

Box 210 is the company's gross chargeable gains, box 215 the allowable capital losses set against them and box 220 the net gain; box 205 catches income that fits no other heading.

If you complete box 210 or 215, HMRC asks you to attach a calculation of each chargeable gain and allowable loss.

Source: HMRC Company Tax Return guide — Other income and chargeable gains

Which boxes cover trading losses?

A trading loss arising in the period goes in box 780; losses set against total profits go in box 275 (this or a later period's loss) and box 285 (losses carried forward).

Trading losses brought forward that can only be used against profits of the same trade go in box 160. HMRC asks for computations that show how losses were used in the period and what is carried forward.

Source: HMRC Company Tax Return guide — Trading losses | Guide: Company made a loss? Your CT600 still needs a loss schedule

How do the boxes add up to the profits chargeable to Corporation Tax?

Box 235 totals the income and gains, box 295 totals the deductions and reliefs, and box 315 — profits chargeable to Corporation Tax — is what is left after qualifying donations and group relief.

Source: HMRC Company Tax Return guide — Profits chargeable

Which boxes calculate the tax and marginal relief?

Box 430 is the Corporation Tax on the profits at the rates for the period, box 435 the marginal relief due and box 440 the Corporation Tax chargeable (box 430 minus box 435); box 326 counts associated companies.

Between box 326 and box 430 the form has a table for the profit charged at each rate of tax, and the tax, in each financial year the period falls in. The marginal relief limits are divided by the number of associated companies plus one — so with three associated companies, they are divided by four.

Source: HMRC Company Tax Return guide — Tax calculation and marginal relief · GOV.UK: Marginal Relief for Corporation Tax | Guides: Corporation Tax rates and marginal relief 2026/27 · Associated companies: check your Corporation Tax thresholds

Which boxes show the tax the company has to pay?

Box 475 is the net Corporation Tax liability, box 510 adds other tax such as tax on loans to participators (box 480), and box 528 is the company's self-assessment of tax payable.

Source: HMRC Company Tax Return guide — Tax payable | Guides: Director's loan account: does the company owe you? · Corporation Tax deadlines: when to pay and file

Which boxes cover capital allowances?

The capital allowances boxes record the allowances included in working out trading profits — full expensing in box 688, the annual investment allowance in box 690, the pools in boxes 695 and 705, and structures and buildings in box 711.

Allowances that are not included in working out trading profits or losses — such as those of a property business — go in a separate set of boxes further down the same page. HMRC says you must show how you calculated the allowances and any balancing charges in your computations.

Source: HMRC Company Tax Return guide — Capital allowances | Guide: Company equipment: expense or capital allowance?

Which tick boxes and indicators might apply?

Most indicator boxes are ticked only if they apply — for example quarterly instalment payments (boxes 630 and 631) — while the exporter questions (boxes 616 to 618) are optional.

HMRC shares the answers to the exporter questions, with the business name and address, with the Department for Business and Trade, and says it will not use them for any other purpose.

Source: HMRC Company Tax Return guide — Tick boxes and indicators

Which boxes confirm R&D and creative industry claims?

Boxes 656 to 658 confirm that the forms HMRC needs for an R&D or creative industries claim have been submitted, and box 653 marks a claim by an R&D-intensive small or medium-sized enterprise.

Source: HMRC Company Tax Return guide — R&D and creative industry claims

What does HMRC need to make a repayment?

HMRC asks for the company's bank or building society details on every return, whether or not you think a repayment is due, and only uses the details from your latest return.

Tick box 40 in "About this return" if a repayment is due for the period. HMRC repays an overpayment of more than £100 automatically, and one of £100 or less when you have given bank details; without bank details, it sets a repayment of £100 or less against later periods.

Source: HMRC Company Tax Return guide — Repayments and bank details

Who signs the CT600 declaration?

Boxes 975 to 985 record the name of the person making the declaration, the date and their status, such as director.

The declaration confirms that the information in the return and any supplementary pages is correct and complete to the best of the person's knowledge and belief. The form warns that giving false information, or concealing any part of the company's profits or tax payable, can lead to both the company and the person making the declaration being prosecuted.

Source: HMRC Company Tax Return guide — Declaration | Guide: How to file a CT600 yourself (without an accountant)

Frequently asked questions

Do I have to fill in every box on the CT600?

No. You complete the boxes that apply to the company for the period and leave the rest blank. HMRC's guide gives examples, such as leaving boxes 210, 215 and 220 blank when there were no chargeable gains.

Where do the figures on the CT600 come from?

From the company's accounts for the period and the tax computation that adjusts them for tax. HMRC says you must include computations that show how the figures in the return were calculated from the accounts.

What is the difference between box 430 and box 440?

Box 430 is the Corporation Tax on the profits at the rates for the period, before marginal relief. Box 440 is the Corporation Tax chargeable after taking off any marginal relief in box 435, so the two are the same when no marginal relief is due.

Where do I find the UTR for box 3?

On letters from HMRC, including the notice to file a return: it is the last 10 digits of the 13-digit number at the top. A limited company can also request its Corporation Tax UTR online.

Does a dormant company have to fill in a CT600?

Only if HMRC asks for one. Once HMRC knows a company is dormant for Corporation Tax, it does not need to file a Company Tax Return unless it gets a notice to deliver one; if a notice arrives, the company must file a return even though no tax is due.