Corporation Tax Calculator UK
For a single company with a 12-month accounting period and no associated companies. The £50,000 and £250,000 limits are divided between associated companies and scaled down for shorter accounting periods. Taxable profit is not the same as turnover — it is profit after allowable expenses and reliefs. Figures are estimates, not tax advice.
Corporation Tax rates 2026/27
| Taxable profit | Rate | How it works |
|---|---|---|
| Up to £50,000 | 19% (small profits rate) | Flat 19% on the whole profit |
| £50,001 to £250,000 | 19% rising to 25% | 25% less marginal relief (fraction 3/200) |
| Over £250,000 | 25% (main rate) | Flat 25% on the whole profit |
Corporation Tax runs by financial year, 1 April to 31 March, and the rates for the year from 1 April 2026 are unchanged from the previous year. Before April 2023 there was a single flat rate of 19% for all companies; the two-tier system was reintroduced to raise more from larger profits. The rates apply UK-wide — England, Scotland, Wales and Northern Ireland alike — and cover ordinary trading profits. Ring-fence profits (oil and gas) are taxed differently and are not covered here.
Marginal relief: why the middle band costs 26.5%
Marginal relief stops the tax bill jumping when profit crosses £50,000. Instead of switching from 19% to 25% overnight, the company pays 25% on the whole profit and then subtracts relief of 3/200ths of the gap between £250,000 and its profits. The formula is: relief = 3/200 × (£250,000 − augmented profits). At £50,000 the relief exactly cancels the extra 6%, so the effective rate is 19%. At £250,000 the relief is zero, so the effective rate is 25%. In between, the effective rate climbs smoothly.
The surprise is the marginal rate. Because the relief shrinks by 1.5p for every extra pound of profit, each extra pound inside the band bears 25p of main-rate tax plus 1.5p of lost relief — 26.5% at the margin, higher than the 25% main rate itself. The average rate never goes over 25%, because the profit below £50,000 was charged at 19% to start with. But if you are deciding whether to take on an extra £10,000 of profit in the band, the tax on that £10,000 is £2,650, not £2,500.
Worked examples
| Profit | Tax at headline rate | Marginal relief | Tax due | Effective rate |
|---|---|---|---|---|
| £30,000 | £5,700 (19%) | — | £5,700 | 19.00% |
| £50,000 | £9,500 (19%) | — | £9,500 | 19.00% |
| £100,000 | £25,000 (25%) | −£2,250 | £22,750 | 22.75% |
| £150,000 | £37,500 (25%) | −£1,500 | £36,000 | 24.00% |
| £200,000 | £50,000 (25%) | −£750 | £49,250 | 24.63% |
| £250,000 | £62,500 (25%) | — | £62,500 | 25.00% |
| £500,000 | £125,000 (25%) | — | £125,000 | 25.00% |
Check the £100,000 row by hand: 25% of £100,000 is £25,000. Marginal relief is 3/200 × (£250,000 − £100,000) = 0.015 × £150,000 = £2,250. Tax due is £25,000 − £2,250 = £22,750. One more, at the bottom of the band: on £60,000 of profit, 25% is £15,000, relief is 3/200 × £190,000 = £2,850, so the tax is £12,150 — an effective rate of 20.25%, barely above the 19% small-profits rate. The taper is gentle at the bottom of the band and steep at the top: that is the whole point of marginal relief, and it is why a company just over £50,000 of profit pays almost the same rate as a company just under it.
Associated companies and short accounting periods
The £50,000 and £250,000 limits are for a standalone company. If your company has associated companies — broadly, companies under common control — the limits are divided by the number of associated companies plus one. Two associated companies means the small-profits limit is £25,000 and the main-rate limit is £125,000 for each of them. The limits are also scaled down proportionately for accounting periods shorter than 12 months. Both adjustments can push a company into marginal relief or the main rate sooner than the headline figures suggest. The limits are tested against augmented profits, which is taxable profit plus most exempt dividends received from companies outside the group.
Deadlines: when Corporation Tax is paid and filed
Corporation Tax is usually due 9 months and 1 day after the end of your accounting period. A company with a 31 March 2027 year end pays by 1 January 2028. The Company Tax Return (form CT600) must be filed within 12 months of the end of the accounting period. Large companies pay in quarterly instalments instead — the threshold for that is profits over £1.5 million, or lower if the company is part of a large group. Late payment carries interest, and late filing carries penalties that grow with the delay, so diary both dates.
If your accounting period straddles 1 April and the rates change in a future year, the profit is apportioned between the two financial years and each slice is taxed at the rate in force for that slice. The rates for the year from 1 April 2026 are the same as the previous year, so a period straddling 1 April 2026 gives the same answer either way — but keep the rule in mind for future years, because the Treasury has changed these rates before and may do so again.
For contractors and directors, the corporation tax figure is only half the story. The company pays this tax on its profits, and then you pay dividend tax personally on what you take out — 8.75%, 33.75% or 39.35% above the £500 allowance. Our dividend tax calculator works out the second layer, and the IR35 calculator runs the whole comparison for contractors.
What counts as taxable profit?
Taxable profit is not the same as the profit in your accounts. You start with the accounting profit, then adjust it. Some expenses in the accounts are not allowable for tax and are added back: business entertaining, fines and penalties, and the private-use share of anything mixed between business and personal use. Other items are deducted that never appear as an expense: capital allowances on plant and machinery, which replace depreciation (depreciation itself is added back and the allowance claimed instead). The main-rate writing-down allowance for plant and machinery fell from 18% to 14% from April 2026, which makes the timing of equipment purchases matter more than it used to.
Directors’ salaries and employer National Insurance are allowable expenses, so paying a salary reduces the company’s taxable profit — which is the other side of the salary-versus-dividends decision. Dividends are not an expense and do not reduce taxable profit. Trading losses can be carried forward against future profits of the same trade, or in some cases carried back or set against other income, which is why a bad year can cut the next year’s bill. The practical point is that the profit figure you type into the calculator should be the taxable profit after these adjustments, not the turnover and not the bank balance. If you are unsure, your year-end accounts from your accountant will state it.
Related: Dividend Tax Calculator · IR35 Calculator · Income Tax Calculator 2026/27
Sources: GOV.UK “Corporation Tax rates and reliefs” (19% small profits rate to £50,000; 25% main rate from £250,000); HMRC Company Taxation Manual CTM03925 (marginal relief formula, fraction 3/200); GOV.UK “Pay Corporation Tax” and “File your Company Tax Return” (deadlines). Checked 13 November 2026.