Free Corporation Tax Calculator

How Corporation Tax is calculated in 2024/25

UK Corporation Tax uses a three-part system for company profits:

Taxable profit	Rate
Up to £50,000 (the lower limit)	19% — small profits rate
£50,000 to £250,000	25% less marginal relief
Over £250,000 (the upper limit)	25% — main rate

In the middle band you pay the 25% main rate reduced by marginal relief, which produces an effective rate that rises smoothly from 19% toward 25%. Marginal relief is the standard fraction of 3/200 multiplied by the gap between your profits and the upper limit. Our guide to Corporation Tax rates and marginal relief walks through the formula with worked examples.

Two things change the limits: the £50,000 and £250,000 thresholds are divided between associated companies (companies under common control), and they are reduced for accounting periods shorter than 12 months. This calculator applies both automatically.

Remember the calculator works from your taxable profit — the figure after tax adjustments such as add-backs for depreciation, capital allowances and disallowable costs. See what a CT600 is and how to file one, and the payment and filing deadlines.

Frequently asked questions

How is Corporation Tax calculated?

Corporation Tax is charged on your company's taxable total profits for the accounting period. For profits up to £50,000 the small profits rate of 19% applies; above £250,000 the main rate of 25% applies; between the two you pay the 25% main rate reduced by marginal relief. Both limits are shared between associated companies and reduced for periods shorter than 12 months.

What is marginal relief?

Marginal relief eases the jump from 19% to 25% for profits between £50,000 and £250,000. It is calculated as the standard fraction (3/200) × (upper limit − augmented profits) × (taxable profits ÷ augmented profits), and is deducted from the tax charged at the main rate, giving an effective rate between 19% and 25%.

What are the Corporation Tax rates for 2024/25?

For financial years 2023 to 2026 the main rate is 25%, the small profits rate is 19%, the lower limit is £50,000, the upper limit is £250,000 and the marginal relief standard fraction is 3/200. Always confirm the current figures on GOV.UK before filing.

How do associated companies affect the calculation?

The £50,000 and £250,000 limits are divided by the number of associated companies plus one. For example, with one associated company the limits halve to £25,000 and £125,000, so marginal relief and the main rate start at lower profit levels.

What if my accounting period is shorter than 12 months?

The lower and upper limits are reduced in proportion to the length of the period (on a 365-day basis), so a six-month period uses roughly half the limits. A full 12-month period keeps the full limits. This calculator applies that automatically from the dates you enter.

Can I file my return with this figure?

This is an estimate for a straightforward non-ring-fence company and excludes reliefs and adjustments such as capital allowances, R&D, losses and franked investment income. For the exact figure and to actually file your CT600 and accounts, prepare your return with Taxley.

When do I pay and file my Corporation Tax?

You must pay within 9 months and 1 day of the end of your accounting period, and file your Company Tax Return (CT600) within 12 months. The payment deadline falls before the filing deadline.