UK Self-Employed Tax Guide: Expenses, Payments & Self Assessment
UK self-employment tax starts with accurate records of business income and allowable costs. Sole traders usually report their profit through Self Assessment. Tax year, accounting basis, business structure and other income can affect the final bill. This guide helps you organize your records and plan ahead; check current HMRC guidance for your circumstances.
How taxable business profit is calculated
Turnover is not the same as taxable profit. Start with business income, then subtract only expenses permitted by HMRC. Costs need a business purpose; mixed-use items require an appropriate personal-use adjustment. Some purchases are capital assets rather than day-to-day costs, and cash basis or traditional accounting may change how income and expenses are recognized. Keep invoices, receipts and clear notes on the work connection.
| Record | Why it matters |
|---|---|
| Sales invoices and receipts | Reconcile gross business income |
| Expense receipts | Substantiate eligible running costs |
| Mileage or usage logs | Support business-use proportions |
| Asset purchase details | Determine capital treatment and relief |
Income Tax, National Insurance and payments on account
Taxable profit can affect Income Tax and National Insurance. PAYE income, rental income, pension contributions and reliefs may alter your overall liability. Some Self Assessment taxpayers make payments on account, usually advance payments toward a later bill. They are credited against the eventual liability, but can create a cash-flow squeeze when you first enter the system. Estimate the combined bill regularly and set aside a portion of each payment received.
Registration, filing and practical workflow
- Check whether your activity requires Self Assessment registration and register by HMRC’s deadline.
- Reconcile invoices, cash, card and platform receipts against bank deposits.
- Separate personal and business costs; annotate mixed-use amounts and capital purchases.
- Review tax and National Insurance estimates through the year, not only in January.
- Check the filing and payment dates for the correct tax year, including any payments on account.
- Seek advice if you operate through a company, hire staff, earn overseas income or have complex losses.
General information only; tax rules change and depend on personal circumstances. Verify current HMRC guidance or consult a qualified adviser.