What is Corporation Tax Calculator?
The Corporation Tax Calculator is a free, no-sign-up web tool designed for UK limited companies to work out their corporation tax liability for the 2026/27 tax year. It goes beyond a simple flat-rate calculation by incorporating the full marginal relief band for profits between £50,000 and £250,000, giving you the effective tax rate, profit after tax, and a clear breakdown of the three profit bands. The tool also calculates payment and filing deadlines based on your accounting period end date, making it a practical companion for year-end planning.
Who it's for
- Small business owners — who need a quick, accurate estimate of their tax bill without digging through HMRC guidance.
- Accountants and bookkeepers — who want a reliable sanity-check tool for client calculations, especially when associated companies complicate the thresholds.
- Company directors planning extraction strategies — who are weighing salary vs dividend decisions and need to see how different profit levels affect the effective tax rate.
Key features
Marginal relief band calculation
The calculator applies the full marginal relief formula for profits between £50,000 and £250,000, so you see the effective rate taper smoothly from 19% up to 25%. It shows the actual tax payable, not just a headline rate, and includes a worked example to explain how the relief is computed.
Associated company threshold adjustment
If your company has associated companies, the £50,000 and £250,000 thresholds are divided automatically. Enter the number of associates, and the calculator adjusts the bands accordingly — essential for groups where the small profits threshold can drop dramatically.
Payment and filing deadline calculator
Enter your accounting period end date and estimated taxable profit, and the tool tells you when your corporation tax payment and filing are due. Most small companies must pay within 9 months and 1 day of year-end, and this feature removes the guesswork.
Side-by-side scenario planner
Compare your current profit level against two alternative scenarios — useful for modelling the impact of investment timing, group restructuring, or changes in dividend policy. Each scenario shows tax, effective rate, and profit after tax, so you can see the marginal cost of each extra pound.
What stands out
Calculate your corporation tax with full marginal relief for profits between £50,000 and £250,000.
Most free calculators stop at a flat 19% or 25% rate, but this one handles the messy middle band properly. The marginal relief formula is transparently explained, and the associated company adjustment means you're not misled by thresholds that don't apply to your situation. The deadline calculator and scenario planner turn a simple tax tool into a mini planning dashboard.
Worth checking out if…
You're a UK company director or accountant who wants a free, accurate estimate of corporation tax for 2026/27 without signing up or wading through spreadsheets. It's especially valuable if you have associated companies, need to plan around the 26.5% marginal rate in the relief band, or simply want to see your effective rate at a glance before making financial decisions.
