Corporation Tax Calculator
Calculate UK Corporation Tax for 2025/26 including marginal relief in the £50k–£250k range.
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What is Corporation Tax?
Corporation Tax is the UK tax on Ltd company profits. It's charged on the company's "taxable profit" — accounting profit plus/minus various tax adjustments (capital allowances, disallowable expenses, etc.). Filed via the CT600 return.
Three rates from April 2023:
- Small profits rate 19% — profits up to £50,000
- Main rate 25% — profits over £250,000
- Marginal relief tapers between the two
Corporation Tax rates and marginal relief
| Profit band | Effective rate |
|---|---|
| £0 – £50,000 | 19% (small profits) |
| £50,001 – £250,000 | Sliding 19% – 26.5% (marginal relief) |
| £250,001+ | 25% (main) |
Marginal relief formula: (Upper Limit − Profit) × 3 ÷ 200 × (Upper Limit ÷ Profit).
Important: the £50k and £250k limits are divided by (associated companies + 1). If you have 2 sister companies, your small-profits limit drops to £16,667 each.
CT deadlines
- Pay — 9 months and 1 day after accounting period end
- File CT600 — 12 months after accounting period end
- Quarterly instalments apply once profits exceed £1.5m (paid up-front, partly during the year)
CT planning
- Annual Investment Allowance — full deduction on equipment up to £1m/year
- R&D Tax Credits — 86% additional deduction (or 14.5% payable credit) for qualifying R&D
- Director's salary at NI threshold — fully deductible, builds state pension
- Pension contributions from the company — fully deductible
- Carry losses forward / sideways / back — set against same-trade or group profits
- Group relief — surrender losses between 75%-owned group members
What this calculator does and doesn't do
- Small profits rate 19% on profits up to £50k
- Main rate 25% on profits above £250k
- Marginal relief between £50k and £250k — formula: (Upper − Profit) × (3 ÷ 200) × (Upper ÷ Profit)
- Thresholds divided by (number of associated companies + 1)
- Doesn't include capital allowances, R&D credits, group relief or losses brought forward
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