Self Assessment tax returns: the 2025/26 guide (deadlines, who files, penalties)

Self Assessment is the system HMRC uses to collect Income Tax from people whose tax isn't taken at source through PAYE. Around 12 million people file a Self Assessment return each year — typically the self-employed, landlords, company directors with untaxed income (such as dividends above the £500 allowance), and higher earners. You report all of your taxable income for the tax year (6 April to 5 April), HMRC calculates what's due, and you pay any balance by 31 January after the tax year ends.

You generally need to file a 2025/26 return if any of the following applied: you were self-employed with gross trading income over £1,000; you were a company director with untaxed income such as dividends above the £500 allowance; you had property income over £1,000; your total taxable income was over £150,000; you had Capital Gains Tax to pay (gains above the £3,000 exempt amount); the High Income Child Benefit Charge applied (income £60,000–£80,000); you had significant untaxed savings, investment or foreign income; or HMRC sent you a notice to file. If you receive a notice, you must file even if you owe no tax — unless HMRC agrees to withdraw it.

For the 2025/26 tax year (which ended 5 April 2026): register by 5 October 2026 if it's your first time, file a paper return by 31 October 2026, or file online and pay any tax owed by 31 January 2027. The 31 January 2027 date is also when your first payment on account for 2026/27 is due, with a second payment on account on 31 July 2027. Filing online gives you three extra months over paper.

HMRC charges an automatic £100 penalty as soon as you miss the 31 January online filing deadline — even if you owe no tax or are due a refund. After three months, daily penalties of £10 apply (up to £900). After six months, you're charged a further £300 or 5% of the tax due, whichever is greater, and the same again after twelve months. Late payment of tax is penalised separately — 5% surcharges at 30 days, 6 months, and 12 months, plus interest on the unpaid amount.

The £100 penalty is HMRC's fixed, automatic late-filing charge that triggers immediately after the 31 January online deadline. It applies even if you owe nothing or are owed a refund, and even if you registered late. It can be cancelled if you appeal and have a genuine 'reasonable excuse' such as serious illness or bereavement — but it is not discretionary in any other circumstances. Filing the return on time, even with an estimated number you correct later, avoids it.

Payments on account are advance payments toward your next year's tax bill. They apply if your Self Assessment bill is over £1,000 and less than 80% of your tax was collected at source. You pay your current bill plus a first payment on account equal to 50% of it (both due 31 January), then a second 50% on 31 July. So a first £3,000 bill becomes £4,500 due on 31 January 2027 plus £1,500 on 31 July 2027. It's not extra tax — you're paying ahead — but the cash-flow hit catches almost every first-time filer by surprise.

Register with HMRC by 5 October after the end of the tax year you need to file for. You choose the right route: form CWF1 if you're self-employed, SA1 if you're not self-employed (a director or landlord, for example), or SA401 if you're a partner. HMRC then posts your Unique Taxpayer Reference (UTR), which typically takes 2–3 weeks. You'll also need a Government Gateway account, your National Insurance number, and records of all income and expenses. You can't file without a UTR, which is why leaving registration late is risky.

Not automatically. Being a director by itself is not a filing requirement. Most directors file because they receive untaxed income — typically dividends above the £500 allowance, which must be reported and taxed through Self Assessment. You report your salary (already taxed via PAYE), your dividends, and any other income. Dividend tax in 2026/27 is 10.75% / 35.75% / 39.35% above the £500 allowance. If all your income were taxed through PAYE with nothing else, you might not need to file.

Yes — HMRC's online filing service is free and many people with simple affairs (a single source of income, straightforward expenses) file their own return. It gets harder with multiple income streams, rental property, capital gains, foreign income, dividends from your own company, or claims for less common reliefs. The risks of filing yourself are missed allowances, incorrect figures triggering an enquiry, and underestimating payments on account. An accountant typically pays for themselves where the return is more than basic.

From 6 April 2026, self-employed people and landlords with qualifying income over £50,000 stop filing the traditional annual Self Assessment return for that income. Instead, they keep digital records and submit quarterly updates plus a Final Declaration under Making Tax Digital for Income Tax. The threshold drops to £30,000 from April 2027 and £20,000 from April 2028. The 2025/26 return many higher earners file by 31 January 2027 is their last legacy Self Assessment. Personal tax not covered by MTD (e.g. dividends from your own company) is still reported through the normal Self Assessment route.