Do I need to file a UK tax return? (And when it's worth filing one anyway)

Most employees in the UK never file a tax return: PAYE takes the right tax from their pay. But plenty of people do need to, often without realising, and some of the most valuable reliefs can only be claimed through a return.

When you must file

For the tax year just gone, gov.uk says you must send a return if you:

• were self-employed as a sole trader and earned more than £1,000 before expenses;
• were a partner in a business partnership;
• have Capital Gains Tax to pay, for example on shares or a property you sold at a profit;
• have to pay the High Income Child Benefit Charge and don't pay it through PAYE;
• got a notice from HMRC asking you to file.

When you may need to

If you had income that wasn't taxed at source, you may need to file. Common examples are rent (including from a property back home), tips and commission, savings interest and dividends above your allowances, and income from abroad. If the amount is small, HMRC can sometimes collect the tax through your tax code instead: use the checker on gov.uk or ask HMRC.

When it's worth filing anyway

Some reliefs only happen if you claim them, and the return is how:

• Higher-rate relief on pension contributions you make yourself (not through salary sacrifice).
• Higher-rate relief on Gift Aid donations.
• The new-arrival reliefs. If you moved to the UK in the last four tax years after ten years away, you can claim to leave out of UK tax your foreign income and gains, and the pay for days you worked outside the UK. Both are claimed only on a return, and both cost you your personal allowance for that year, so check the numbers first.

How to register and file

Register for Self Assessment on gov.uk by 5 October after the tax year ends; you'll get a UTR by post. The online return and any tax due are due by 31 January. See the 31 January deadline for what happens if you miss it.