Your company pays an estimated £22,750 in Corporation Tax on £100,000 of taxable profit in the illustration below. This calculator estimates tax for one eligible UK resident company, adjusting the profit limits for other associated companies and a shorter accounting period.
It uses financial year 2026 rates for a period wholly within 1 April 2026 to 31 March 2027. Enter taxable profit after tax adjustments and any loss relief already claimed, rather than sales, bank receipts or an unadjusted accounting profit.
How Corporation Tax is calculated
For an eligible company with a 12 month period and no other associated companies, the small profits rate is 19 per cent on profits up to £50,000. The main rate is 25 per cent at or above £250,000. Between these limits, marginal relief reduces the tax calculated at the main rate.
Marginal relief makes the effective rate, meaning tax divided by taxable profit, increase gradually between the two rates. These are not income tax bands: the calculator does not tax separate slices of company profit at each headline rate.
Marginal relief explained
This tool assumes augmented profits equal taxable profits. Augmented profits are the profit measure used for these limits and can include certain distributions received by the company. Under this assumption, marginal relief is 0.015 multiplied by the difference between the adjusted upper limit and taxable profit. The calculator subtracts that relief from tax at the main rate.
If distributions increase your augmented profits, this simplified calculation is unsuitable. The tool also assumes that your company is eligible for the small profits rate and marginal relief. Read the government guidance on marginal relief eligibility.
Illustration: an e-commerce company
This is an illustration, not a client example. An eligible UK resident online retailer has £100,000 of taxable profit for the 12 months ending 31 March 2027, no other associated companies and no distributions that increase augmented profits.
25 per cent of £100,000 is £25,000. The upper limit less profit is £250,000 minus £100,000, which equals £150,000. Multiplying this difference by 0.015 gives marginal relief of £2,250. Tax is therefore £25,000 minus £2,250, which equals £22,750. The effective rate is 22.75 per cent.
Associated companies reduce the limits
Enter the number of other associated companies, excluding the company being calculated. Both limits are divided by one plus that number. Confirm which companies count before using the result; this tool does not determine association and assumes the count remains constant throughout the period.
Illustration: with one other associated company and a full accounting year, the lower limit becomes £25,000 and the upper limit becomes £125,000. On the same £100,000 profit, marginal relief is £375 and estimated tax is £24,625.
Short accounting periods
The calculator multiplies both limits by the number of months divided by 12, then divides them by one plus the number of other associated companies. Enter the actual taxable profit for the short period. The tool scales the limits, not the profit.
Whole-month scaling is an estimate. It does not calculate exact calendar-day apportionment or split a period across financial years. Do not use this tool for a period that straddles 1 April.
When payment and filing are due
Corporation Tax is normally payable 9 months and 1 day after the accounting period ends. The Company Tax Return is normally due 12 months after the period ends. Payment and filing are separate obligations. Companies within quarterly instalment rules have different payment deadlines, which this tool does not assess.
Read our guide to how and when to pay Corporation Tax for the payment process.
What this calculator does not do
It does not model periods straddling 1 April, ring fence profits from oil rights or extraction, quarterly instalments, non-UK resident companies or close investment holding companies. It does not establish relief eligibility, calculate losses or allowances, or handle distributions that increase augmented profits. Monetary results are rounded to pennies, while adjusted limits remain unrounded during calculation.
For help checking taxable profit and preparing a return, see our Corporation Tax service.
Frequently asked questions
What Corporation Tax rates does this calculator use?
For financial year 2026, it uses the 19 per cent small profits rate and the 25 per cent main rate. Before adjustments, the lower profit limit is £50,000 and the upper limit is £250,000. Marginal relief applies between the limits for eligible companies.
How does the calculator work out marginal relief?
It assumes augmented profits equal taxable profits. Between the adjusted limits, it multiplies the adjusted upper limit minus taxable profit by 0.015, then subtracts that relief from tax at the main rate. If distributions increase augmented profits, this simplified calculation is unsuitable.
How do associated companies affect Corporation Tax?
Both profit limits are divided by one plus the number of other associated companies. With one other associated company and a full accounting year, the limits become £25,000 and £125,000. The calculator assumes the count stays constant throughout the period.
Can I calculate tax for a short accounting period?
Yes. Choose a whole number of months from 1 to 12 and enter the taxable profit for that period. The calculator scales both limits by months divided by 12. This is a whole-month estimate and does not calculate exact calendar-day apportionment.
When are Corporation Tax payment and filing due?
Payment is normally due 9 months and 1 day after the accounting period ends. The Company Tax Return is normally due 12 months after the period ends. Companies required to pay quarterly instalments have different payment deadlines. This tool does not assess instalment obligations.
Should I enter turnover or profit?
Enter taxable profit for the accounting period after tax adjustments and any loss relief already claimed. Do not enter turnover or bank receipts. The tool does not calculate taxable profit from your accounts or determine which expenses and reliefs are allowable.
Which companies and accounting periods are outside the scope?
Do not use this tool for periods straddling 1 April, ring fence profits, non-UK resident companies or close investment holding companies. It also excludes distributions that increase augmented profits, changes in the associated company count during the period and quarterly instalment calculations. It covers one eligible accounting period wholly within 1 April 2026 to 31 March 2027.