Self Assessment: deadlines, penalties and who must file

Updated 2026-10-03 · Reviewed against official government sources

Self Assessment is how HMRC collects Income Tax on income that is not taxed at source, such as self-employment profit, rent, large dividends and capital gains. Miss a deadline and penalties start at £100 even if you owe nothing. This guide sets out the key dates for the 2025/26 return (due in January 2027), who has to file, and how the penalty regime works, including the new points-based system for people in Making Tax Digital.

Key dates for the 2025/26 tax year

The 2025/26 tax year ran from 6 April 2025 to 5 April 2026. These are the deadlines that follow from it.

Deadline	What happens
5 October 2026	Register for Self Assessment if you have not filed before
31 October 2026	Paper return deadline
30 December 2026	File online by this date if you want tax under £3,000 collected through your PAYE tax code
31 January 2027	Online return deadline; pay the 2025/26 balance and first 2026/27 payment on account
31 July 2027	Second 2026/27 payment on account
31 January 2028	Last date to amend the 2025/26 return

Who must file a return

You generally need to file if, in the tax year, any of the following applied. HMRC's online checker gives a definite answer.

You were self-employed with gross trading income over £1,000, or were a partner in a partnership.
You had rental income over £10,000 before expenses, or £2,500 or more after expenses.
You had other untaxed income of £2,500 or more, or dividends or savings interest over £10,000.
You made capital gains that are taxable or had disposal proceeds over £50,000 (unless already reported via a UK property return).
You or your partner had adjusted net income over £60,000 and received Child Benefit, unless you pay the charge through PAYE.
You had foreign income to declare, or HMRC sent you a notice to file.

Late filing penalties

These apply to returns outside Making Tax Digital. They are added together, so a return 12 months late can cost at least £1,600 even with no tax due.

How late	Penalty
1 day	£100 fixed penalty
3 months	£10 a day for up to 90 days (maximum £900)
6 months	Further 5% of tax due or £300, whichever is higher
12 months	Further 5% of tax due or £300, whichever is higher (can be up to 100% if information was deliberately withheld)

Late payment penalties and interest

For tax paid late under the current Self Assessment rules, a penalty of 5% of the unpaid tax is charged at 30 days, another 5% at 6 months and another 5% at 12 months. Interest is also charged on late tax and on penalties from the due date. Since 6 April 2025 the late payment interest rate is the Bank of England base rate plus 4 percentage points.

If you cannot pay in full, contact HMRC before the deadline. If you owe £30,000 or less, have no other debts with HMRC and are within 60 days of the deadline, you can usually set up a Time to Pay plan online. A plan agreed before a penalty date stops that late payment penalty.

The new MTD penalty regime

If you are in Making Tax Digital for Income Tax (qualifying income over £50,000 from April 2026), a different system applies. Each late submission earns a penalty point; when you reach the threshold of 4 points you get a £200 penalty, and £200 for each further late submission while at the threshold. There are no penalties for late quarterly updates in 2026/27.

Late payment penalties under MTD are percentage-based. For 2026/27 tax, 3% of tax still unpaid at day 15, another 3% of tax unpaid at day 30, then 10% a year charged daily from day 31. For 2027/28 the two fixed charges rise to 4% each.

Worked example: 4 months late

Tom owes £2,000 for 2025/26. He files and pays on 30 May 2027, about four months after the deadline.

Late filing: £100 + 30 days of daily penalties from 1 May (£10 x 30 = £300) = £400
Late payment: 5% of £2,000 at 30 days = £100
Plus interest on £2,000 from 31 January at base rate + 4%
Total penalties: £500 before interest

Appealing a penalty

You can appeal within 30 days of the penalty notice if you had a reasonable excuse, such as serious illness, a bereavement, or an HMRC system failure, and you filed as soon as the problem ended. Forgetting, or not having the money, does not count. If you no longer need to file, ask HMRC to withdraw the notice to file rather than leaving it.

Your first return: cash flow in the first January

Your first January bill can be about one and a half times the year's tax, because the first payment on account for the next year is due on the same day.

A sole trader in England who starts in April 2026 with £40,000 profit owes £7,131.80 for 2026/27 (income tax £5,486.00 plus Class 4 NI £1,645.80). On 31 January 2028 they pay that plus a first payment on account of £3,565.90, a total of £10,697.70. A further £3,565.90 is due on 31 July 2028. Setting aside about 27% of profit in year one avoids the shock.

Correcting a return after you file

You can amend a return online for 12 months after the 31 January deadline, so the 2025/26 return can be changed until 31 January 2028. After that, you must write to HMRC to report an underpayment or claim back an overpayment.

After the amendment window closes, you can still claim overpayment relief for tax paid in error, generally within 4 years of the end of the tax year. Keep records for at least 5 years after the 31 January deadline if you are self-employed or a landlord, or 22 months after the end of the tax year otherwise. The 22-month rule assumes the return was filed on time; GOV.UK gives longer periods for late returns.

Related calculators & guides

Frequently asked questions

When is the Self Assessment deadline?

For the 2025/26 tax year, online returns and payment are due by 31 January 2027. Paper returns were due by 31 October 2026.

What is the penalty for a late tax return?

£100 immediately, then £10 a day after 3 months (up to £900), then the higher of 5% or £300 at 6 and 12 months. Late payment adds 5% at 30 days, 6 months and 12 months, plus interest.

Do I pay a penalty if I owe no tax?

Yes, the £100 late filing penalty applies even if no tax is due. You can ask HMRC to cancel the notice to file if you did not need to file.

Do I need to file Self Assessment if I earn over £150,000?

Not just for that reason. The £150,000 rule was removed from 2023/24. PAYE-only employees file only if another criterion applies.

What is a payment on account?

An advance payment towards next year's tax, each half of last year's bill, due on 31 January and 31 July. It applies if your bill exceeded £1,000 and under 80% was taxed at source.

How does the MTD penalty system differ?

It uses points for late submissions (£200 at 4 points) and percentage late payment penalties (3% at day 15, 3% at day 30 and 10% a year after that for 2026/27).

Can I pay my tax bill in instalments?

Yes, with a Time to Pay arrangement. Online plans are available for debts up to £30,000. Interest still applies.

How much will my first Self Assessment bill be?

Often about 150% of the year's tax, because the first payment on account for the next year (half the bill) is due on the same 31 January.

How long can I amend my tax return?

Up to 12 months after the 31 January filing deadline. For 2025/26 returns that is 31 January 2028.

How long must I keep Self Assessment records?

At least 22 months after the end of the tax year, or 5 years after the 31 January deadline if you are self-employed or let property.

Sources

Figures are taken from official government publications and were last reviewed on 2026-10-03.