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Corporation Tax Calculator 2025/26

Free UK Corporation Tax calculator with marginal relief for 2025/26. 19% small profits rate, 25% main rate, full marginal relief workings.

Corporation Tax due£17,450On £80,000 of taxable profit
  • Taxable profit£80,000.00
  • Main rate (25%)£80,000 × 25%£20,000.00
  • Marginal relief(£250,000 − £80,000) × 3/200£2,550.00
  • Total Corporation TaxEffective rate: 21.81%£17,450.00

2024/25 rates: 19% on profits up to £50,000, 25% on profits over £250,000, with marginal relief between. Associated companies divide both thresholds proportionally. Excludes R&D credits and special regimes.
How this is calculated

The maths, in plain English.

UK Corporation Tax for 2025/26 has two rates with marginal relief between them:

  • Small profits rate (19%) — profits up to £50,000
  • Main rate (25%) — profits over £250,000
  • Marginal relief — between £50,000 and £250,000, an effective rate that smoothly increases from 19% to 25%

Both thresholds are divided by the number of associated companies plus one. So with no associates, you keep the full thresholds; with two associates, each company has £16,667 / £83,333 thresholds.

The formula for marginal relief is: (Upper Limit − Profit) × 3/200. This is subtracted from the headline 25% tax.

This calculator covers standard trading profits. R&D Tax Credits, Patent Box, capital allowances, and tax losses can all change the picture significantly — get in touch for a full review.

Common questions

4 questions we get asked.

If yours is not here, ring us. We answer in four rings on weekdays and write back the same day on emails.

01 What is marginal relief?
Between £50,000 and £250,000 of taxable profit, you pay 25% main rate but get a discount that effectively averages your rate between 19% and 25%. The formula is: (£250,000 − profit) × 3/200. The result reduces the 25% headline tax.
02 What are associated companies?
Companies under common control share the £50,000 / £250,000 thresholds. So if you control two companies, each gets £25,000 / £125,000 thresholds. This stops people splitting one big company into many small ones to dodge the main rate.
03 When is Corporation Tax due?
Most companies must pay Corporation Tax 9 months and 1 day after their accounting period end. The CT600 return must be filed within 12 months. Larger companies (profits over £1.5m generally) pay quarterly instalments instead.
04 Can R&D credits reduce my Corporation Tax?
Yes — significantly. From April 2024, loss-making R&D-intensive SMEs can claim back roughly 18.6% of qualifying spend as cash. Profit-making SMEs see effective tax savings of around 21.5% on qualifying R&D. We handle R&D claims for our tech and innovation clients regularly.
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