Use this free UK corporation tax calculator to estimate how much Corporation Tax your limited company may owe based on taxable profits, augmented profits, and associated companies. It is designed for quick planning and budgeting.
How this UK corporation tax calculator works
For most companies, UK Corporation Tax is now based on a small profits rate, a main rate, and marginal relief in between. This calculator follows that structure for planning purposes:
- Small profits rate: 19%
- Main rate: 25%
- Lower limit: £50,000 (divided by total associated companies)
- Upper limit: £250,000 (divided by total associated companies)
If your profits are between the lower and upper limits, marginal relief applies. The result is a gradual effective rate between 19% and 25%, rather than a sudden jump.
What are taxable profits?
Taxable profits are not simply your accounting profit. In practice, your final Corporation Tax figure is based on profits after tax adjustments. Common adjustments include:
- Disallowing non-deductible expenses
- Claiming capital allowances
- Using brought-forward losses where available
- Applying relevant reliefs and elections
Because of these adjustments, always treat online results as an estimate until your tax computation is prepared.
What are augmented profits?
Augmented profits are used to test where your company sits in the Corporation Tax banding. A simple rule of thumb is: taxable profits plus franked investment income (for example, dividends from non-group companies).
If you leave augmented profits blank in the calculator, it assumes augmented profits equal taxable profits.
Associated companies and threshold reduction
If your company has associated companies, the £50,000 and £250,000 thresholds are divided. This is important and often missed in rough estimates.
Example: if your company has 2 associated companies, total companies in the group for threshold purposes is 3.
- Adjusted lower limit: £50,000 ÷ 3 = £16,666.67
- Adjusted upper limit: £250,000 ÷ 3 = £83,333.33
This can push companies into marginal relief or main rate much earlier than expected.
Example calculation (quick illustration)
Suppose:
- Taxable profits = £90,000
- Augmented profits = £90,000
- Associated companies = 0
Your profits sit between £50,000 and £250,000, so marginal relief applies. The calculator computes main-rate tax first and then deducts marginal relief. The final effective rate is above 19% but below 25%.
Important deadlines for UK limited companies
- Corporation Tax payment: usually due 9 months and 1 day after the end of your accounting period.
- Company Tax Return (CT600): usually due 12 months after your accounting period ends.
- Accounts filing: deadlines at Companies House are separate and still apply.
Missing deadlines can trigger penalties and interest, so use your estimate early to support cash-flow planning.
Calculator limitations
This tool is for education and planning. It does not replace tailored advice. It does not cover every edge case, including:
- Ring-fenced profits (for certain industries)
- Research and Development (R&D) relief interactions
- Quarterly instalment payment rules for very large companies
- Complex group and distribution structures
If your numbers are material, ask a qualified UK tax adviser or accountant to review your full computation before filing.