Self Assessment is how self employed people and others with untaxed income report earnings and pay tax to HMRC. This guide covers who needs to file, the deadlines, and how the bill is worked out.
Published July 2026 · Updated July 2026
Self Assessment is the process where you tell HMRC about income that has not already been taxed, and HMRC works out the Income Tax and National Insurance due. Employees are usually taxed automatically through PAYE, but the self employed report their own figures.
You typically need to file if you were self employed and earned more than £1,000, rented out property, or had other untaxed income such as dividends above the allowance. Some higher earners and company directors also file.
The tax year runs to 5 April. For that year, the online return and the balancing payment are due by the following 31 January. Paper returns are due earlier, by 31 October.
If your bill is over £1,000, HMRC usually asks for 'payments on account', two advance instalments towards next year's tax, due 31 January and 31 July. This can make your first January bill larger than expected.
You are self employed with £31,000 of taxable profit for 2025/26:
By 5 October following the end of the tax year in which you started earning untaxed income, so HMRC can set up your record in time.
Records of your income and allowable expenses. Keeping them digitally makes filing quicker and is required once MTD for Income Tax applies to you.
There is usually an automatic £100 penalty, with further penalties and interest the longer it is outstanding.
Source: GOV.UK ↗. This glossary is written for small business owners, so definitions are simplified. Tax rates and thresholds reflect 2026/27 UK rules and change over time. Berified does not provide accounting, tax or legal advice; always check the source or a qualified adviser.