Open Corporation Tax from the period menu. The headline Corp Tax Payable figure at the top recalculates the moment you change anything, and the Sections menu beneath it breaks the computation into focused screens. The menu starts with the sections almost every company uses: General, P & L, Accounting Adjustment, Assets, Loan to Participators, R & D Expenditure, Donations, Losses and Repayments. Everything else is added when you need it: click Add Section at the bottom of the menu, tick the sections that apply and click Save. A section that already holds figures is always in the menu, marked with a green dot.
You won't need every section — work down the list and complete the ones that apply.
General
Start here. Check the CT return period matches the accounting period (it's split automatically if your accounts run longer than twelve months — see Accounting periods longer than 12 months), answer the group and filing questions — associated companies, estimated figures, group payment arrangements — and choose the director accepting the declaration. The number of associated companies matters: it scales down the marginal relief limits that decide your tax rate.
Further down, answer Did the company export in this period? — select Goods, Services or both, or Neither. HMRC asks every company this question (CT600 boxes 616 to 618), and the submission wizard warns you if it is left unanswered.
If the company’s profits are large enough to fall under the quarterly instalment rules — broadly more than £1.5 million, shared between associated companies — Tax Optimiser ticks CT600 box 630 (or box 631 above £20 million) automatically and shows a warning on this section, because the instalments themselves are not calculated. Answer Is first year and not large? if the company was not large in the previous twelve months: the limit is then £10 million for the year.
P & L and disallowables
The P&L section lists your profit and loss accounts straight from the trial balance, each with a Disallowable box. Enter the part of each expense that isn't deductible for Corporation Tax — the classic example is client entertaining, which is disallowed in full. Anything you put here is added back to profit in the computation, with a supporting schedule created automatically.
Each line also has a Type dropdown. Leave it at Trade unless the company lets property: rental income and the costs of letting should be set to UK property so they are taxed as a property business (CT600 box 190) rather than in the trade — see UK property income and losses.
Depreciation is the one add-back almost every company needs: enter the whole P&L depreciation charge as Disallowable here, then claim capital allowances in the Assets section (see the next article). Depreciation in your trial balance walks through it end to end, including profits and losses on disposal. Charitable donations, by contrast, do not need adding back here: they are added back and relieved automatically once entered in the Donations section below.
Accounting adjustments
Prior-period and transitional adjustments to taxable profit that aren't simple disallowables — income to recognise back to the accounts, or expense adjustments — live in their own section with separate income and expense tabs.
Donations
Enter qualifying charitable donations here. They're treated exactly as HMRC expects: added back to trading profit, then deducted from total profits to arrive at profits chargeable. Don't also disallow them in the P&L section — that would double-count the add-back. The validate donation total with P&L option cross-checks the section against your trial balance donations row.
Non-trade income, credits and debits
Bank interest receivable from your trial balance is picked up automatically as a non-trading loan relationship credit — taxed, but outside trading profit. The Non Trade Income, Credit and Debit sections let you review what's been routed there and add anything else (for example interest on overpaid tax, or non-trade loan interest payable).
The other sections
Chargeable gains and management expenses
Two sections cover companies that hold investments; add them with Add Section. Chargeable Gains records sales of capital assets such as investment property and shares: the gain on each disposal is calculated, capital losses brought forward are used, and the net gain is added to total profits (CT600 boxes 210 to 220) — see Chargeable gains on the CT600. Management Expenses is for a company with investment business: enter the costs of managing the investments and they are taken out of the trade and deducted from total profits instead (box 245), with any excess carried forward — see Management expenses for investment companies.
The remaining sections follow the same pattern and only need attention when they apply. Loan to Participators (s455 tax on director/shareholder loans), R & D Expenditure and Losses (covered later in this guide) are always in the menu. The rest are added with Add Section: Provision, Car Lease (the flat-rate disallowance for higher-emission leased cars), Creative Industries, Income Tax Suffered (tax deducted at source, box 515, and the gross income it came from, box 185), Double Taxation Relief (credit for foreign tax on overseas income, box 450 — see Double taxation relief on the CT600), Investment Income (exempt dividends, box 620, and non-exempt dividends from overseas companies, box 180 — see Other income on the CT600), Intangibles & Other Reliefs (non-trading intangible fixed assets and non-trade capital allowances, boxes 195, 265 and 290 — see Non-trading intangibles on the CT600) and Tax Avoidance disclosures. The specialist supplementary pages, from Group Relief to Tonnage Tax, are added the same way.
