Self Assessment Tax Return: A Step-by-Step UK Guide

Self Assessment is the system HMRC uses to collect income tax from people who do not have all their tax deducted at source. If you are self-employed, a company director, earn over £150,000, have rental income, or have untaxed income above £2,500, you probably need to file. HMRC will not always write to tell you, so registering is your responsibility.

The key deadlines are: register by 5 October after the end of the tax year, submit a paper return by 31 October, or an online return by 31 January. Payment is also due by 31 January. Late filing triggers an automatic £100 penalty, even if you owe no tax at all. At 3 months late, daily £10 charges start, up to 90 days. At 6 months and 12 months, further penalties of 5% of the tax owed apply on top.

The penalty applies whether or not you owe money. You can owe nothing and still be fined £100 for filing late.

You will need records of all income (employment, self-employment, dividends, rental, interest), allowable expenses, pension contributions, Gift Aid donations, and student loan repayment details. Keeping organised records throughout the year makes January far less stressful. You can file from 6 April onwards, and filing early does not bring your payment date forward. Tax is still due 31 January regardless of when you submit.