Corporation Tax Calculator

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

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