Self-assessment for 2025/26: deadlines, penalties and how to register
Who must file, the 31 October paper and 31 January online deadlines, payments on account and the fines for being late
The 2025/26 tax year ended on 5 April 2026 and the return for it is now due. Paper returns must reach HMRC by 31 October 2026 and online returns by 31 January 2027, the same day the tax is due. If this is your first year, you must register by 5 October 2026 to get set up in time. This guide covers who has to file, what happens if you are late, and the payments on account that surprise many first-time filers.
Who must file
You need a return for 2025/26 if any of these applied between 6 April 2025 and 5 April 2026:
- You were self-employed with gross income over £1,000.
- You received rental income over £1,000 after the property allowance, or over £2,500 in profit.
- You had untaxed income, such as savings interest, dividends or foreign income, that your tax code could not cover.
- Your income was over £150,000.
- You or your partner received Child Benefit and the higher earner's adjusted net income was over £60,000, unless you have moved the charge into your PAYE code.
- You sold assets and owe capital gains tax that has not already been reported.
- You are a company director with untaxed income, or a partner in a business.
If HMRC has sent you a notice to file, you must file even if you think you owe nothing. Ask HMRC to withdraw the notice if you no longer meet the criteria.
How to register
New filers go to gov.uk. Sole traders register for self-assessment and Class 2 National Insurance together. Everyone else registers as "not self-employed". HMRC posts a Unique Taxpayer Reference within a couple of weeks, then you set up a Government Gateway login to file online. Allow a month for the whole process, which is why the 5 October date matters.
If you filed last year you do not need to register again. Your UTR stays the same.
Payments on account
Once your self-assessment bill is over £1,000, and less than 80% of your tax was collected at source, HMRC asks you to pay next year's tax in advance. Each payment on account is half of this year's bill.
| Date | What you pay |
|---|---|
| 31 January 2027 | Balance for 2025/26 plus first payment on account for 2026/27 |
| 31 July 2027 | Second payment on account for 2026/27 |
| 31 January 2028 | Balance for 2026/27 plus first payment for 2027/28 |
In year one this means paying one and a half years' tax in a single go. If you know your income will fall, you can apply to reduce the payments on account, but if you reduce them too far HMRC charges interest on the shortfall.
Penalties for missing the deadlines
Late filing penalties apply even if you owe no tax.
- One day late: £100.
- Three months late: £10 a day for up to 90 days, so up to £900 more.
- Six months late: a further £300 or 5% of the tax due, whichever is higher.
- Twelve months late: another £300 or 5%, and more in serious cases.
Late payment adds 5% of the unpaid tax at 30 days, six months and twelve months, plus daily interest at a rate above the Bank of England base rate. If you cannot pay, set up a Time to Pay arrangement online before 31 January. It avoids the 5% surcharges, though interest still runs.
You can appeal a penalty if you had a reasonable excuse, such as a serious illness or a bereavement, but being busy or not knowing the rules does not count.
What to do next
- If you need to register, do it this week.
- Gather your records: P60, P45, bank interest statements, dividend vouchers, invoices, expense receipts, rental statements and pension contribution certificates.
- File online early. You do not have to pay until 31 January, and an early filing gives you a firm figure to budget for.
- Check whether payments on account will apply and put the July money aside now.
- If you use Making Tax Digital from April 2026, you still file a full return for 2025/26 under the old system. The quarterly updates only start with the 2026/27 year.