Corporation Tax Calculator
Estimate your corporation tax liability using either a UK simplified banded method (19% / marginal relief / 25%) or a custom flat rate.
Note: This tool provides an educational estimate and does not replace professional tax advice. Local rules, reliefs, group structures, and accounting period changes can materially affect your final tax bill.
Why use a corporation tax calculator?
If you run a limited company, your corporation tax bill is one of the biggest financial obligations you plan for each year. A reliable calculator helps you forecast cash flow, avoid surprises, and compare “what-if” scenarios before you commit to major expenses, dividends, or salary changes.
This calculator is built for practical planning. You can enter turnover, allowable expenses, non-deductible costs, capital allowances, and losses brought forward to estimate taxable profit and expected corporation tax.
How the calculator works
1) Build accounting profit
We begin with:
- Turnover minus allowable expenses to get a base profit figure.
2) Apply tax adjustments
Then we adjust that figure for tax purposes:
- Add back non-deductible expenses (costs that are in your accounts but not tax-deductible).
- Subtract capital allowances.
- Subtract losses brought forward used in the period.
The result is your estimated taxable profit. If this value drops below zero, the taxable profit is treated as £0 for this estimate.
3) Apply a tax method
You can choose between:
- UK Simplified: small profits rate, marginal relief band, and main rate.
- Custom Flat Rate: useful for non-UK planning models or internal budgeting assumptions.
UK corporation tax rates (simplified model)
For the UK method, this calculator uses a simplified approach aligned with current headline concepts:
- 19% for profits at or below the lower limit.
- 25% for profits at or above the upper limit.
- Marginal relief between the limits.
If your company has associated companies, lower and upper limits are divided by the number of companies in the group (including your own). The calculator does this automatically using your input.
Input guide: what to enter
Turnover / Total Income
Enter total business income for the accounting period before expenses.
Allowable Expenses
Enter ordinary business costs that are generally deductible for tax, such as office costs, software, wages, and professional fees (where applicable).
Non-deductible Expenses / Add-backs
Examples might include penalties, some entertaining costs, or private use portions not allowable for tax.
Capital Allowances
If you are claiming tax relief on qualifying assets, include the amount of capital allowances claimed in this period.
Losses Brought Forward Used
Enter the amount of prior year losses actually used to reduce current taxable profit.
Practical tax planning ideas
- Keep bookkeeping current so your tax estimate stays accurate month-to-month.
- Review capital expenditure timing before year-end to optimize allowances.
- Check that expenses are correctly categorized between deductible and non-deductible.
- Model different salary/dividend strategies with your accountant.
- Set aside tax monthly to avoid cash pressure at payment deadlines.
Common mistakes to avoid
- Assuming accounting profit and taxable profit are identical.
- Forgetting associated companies can reduce UK thresholds.
- Missing loss relief opportunities due to poor records.
- Using a single tax rate without checking marginal relief rules.
- Treating quick estimates as a final tax return figure.
Frequently asked questions
Is this calculator suitable for final filing numbers?
No. It is designed for planning and education. Your statutory accounts, detailed adjustments, and professional advice determine final filing values.
Does this include every relief and anti-avoidance rule?
No. It does not include every edge case (group relief complexity, sector-specific reliefs, R&D detail, transfer pricing, and many other technical rules).
Can I use this for non-UK entities?
Yes, use the custom flat-rate option for a rough estimate, then validate with local rules for your jurisdiction.
Final thought
A corporation tax calculator is most useful when used regularly, not once a year. Update your numbers quarterly or monthly, compare scenarios, and use the estimate to guide proactive decisions with your accountant. Better forecasting usually means better cash flow, better timing, and fewer year-end surprises.