UK corporation tax calculator.
Enter taxable profit and the number of associated companies. The tool applies the small profits rate, the main rate or marginal relief, and shows the marginal rate on your next pound.
Companies under common control anywhere in the world, excluding dormant ones. Each divides the £50,000 and £250,000 thresholds.
Corporation tax due
Marginal relief band · effective rate 23.4%
Financial year 2026/27 rates, checked September 2026. Excludes reliefs such as full expensing, R&D credits and loss relief, which reduce taxable profit before this calculation. Payment is due nine months and one day after the period end.
What is marginal relief?
A reduction that tapers the rate between 19 and 25 percent for profits between £50,000 and £250,000. The formula is 3/200 of the difference between the upper limit and your profit. Across the band the marginal rate on each extra pound is 26.5 percent.
What is an associated company?
A company under common control with yours, anywhere in the world, at any point in the accounting period. Each one divides the £50,000 and £250,000 limits, so a company with one associate uses £25,000 and £125,000.
When do I pay?
Nine months and one day after the end of the accounting period, for companies with profits under £1.5 million. Above that, quarterly instalments apply.
Have it computed and filed.
We prepare the CT600 from books we already keep, plan the reliefs before year end, and file within the deadline.