Self-employed expenses: common mistakes to avoid

Common expense-related mistakes that lead to the wrong profit input: mixing personal costs, double counting, and inconsistent categories.

• The calculator expects profit after allowable expenses, so expense mistakes distort estimates.
• Start conservative if you are unsure, then verify against official guidance.
• Keep a repeatable method so your estimate improves over time.

Why this matters

Most errors come from inputs, not tax rates. If expenses are wrong, profit is wrong, and your estimate becomes misleading.

Common mistakes

Mixing personal spending into business costs, claiming mixed use items without a method, and failing to keep evidence. These issues can make your estimate look too low.

A safer approach

If something feels unclear, do not force it. Use the calculator for planning and verify the correct treatment using GOV.UK or an accountant.

Not tax advice. This page is an educational guide. For official rules, verify the sources below.

Last updated: 2026-04-20

FAQ

Sources

For official rules and definitions, verify with the references below.

• https://www.gov.uk/expenses-if-youre-self-employed