Your profit is your total business income minus allowable business expenses. This includes costs like equipment, travel, office expenses, and professional fees. Check HMRC's guidance on allowable expenses for your specific situation.

Self Assessment tax returns and payments are due by 31st January following the end of the tax year. You may also need to make payments on account by 31st July if your tax bill exceeds £1,000.

This calculator uses official 2025/26 HMRC tax rates and thresholds. However, it provides estimates only and may not account for all personal circumstances. Always consult with a qualified accountant or HMRC for advice specific to your situation.

Class 4 National Insurance is paid by self-employed people on their annual profits. For 2025/26, you pay 6% on profits between £12,570 and £50,270, and 2% on profits above £50,270. This is separate from Class 2 NI contributions.

The "set aside" percentage tells you what portion of each invoice to save for your tax bill. For example, if your set-aside is 25%, you should save £250 from every £1,000 you earn to ensure you can pay your taxes when they're due.