Turn your accounting profit into a CT600 corporation tax computation: add back disallowable items, deduct allowances and reliefs, and apply the 2025/26 main rate with marginal relief.
Données vérifiées · July 2026
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Starts from your accounting profit and adjusts it into taxable total profits: depreciation is added back (it isn't a tax-deductible cost) and replaced by capital allowances, disallowable expenses (client entertaining, fines) are added back, and R&D deductions and losses brought forward reduce the taxable figure. The result is taxed at 19% up to £50,000, 25% above £250,000, with marginal relief tapering the rate in between — both limits divided by the number of associated companies.
£120,000 accounting profit, £10,000 depreciation add-back, £15,000 capital allowances: £115,000 taxable profit taxed with marginal relief between the two thresholds, giving roughly a 22.75% effective rate.
Enter your accounting profit for the period.
Add back depreciation and any disallowable expenses.
Enter capital allowances, R&D deduction and losses brought forward.
Add the number of associated companies if you have any — it lowers the small-profits and main-rate thresholds.
Last data update
July 7, 2026
Sources and references
HMRC — Corporation Tax rates and reliefs (gov.uk/corporation-tax-rates); Marginal Relief for Corporation Tax (gov.uk/guidance/corporation-tax-marginal-relief), 2025/26.
The data in this calculator is updated regularly to reflect the latest official rates. When in doubt, consult the official sources listed above.
Marginal relief blends the two rates for taxable profits between £50,000 and £250,000 (divided by associated companies), so the effective rate rises smoothly rather than jumping.
No — only items that are not tax-deductible (client entertaining, most fines, depreciation) are added back. Ordinary trading expenses remain deductible.