Self Assessment deadlines and penalties
Online Self Assessment returns are due by 31 January following the end of the tax year, along with any tax owed. Missing it triggers an automatic £100 penalty even if you owe nothing, followed by £10 a day after three months, and further penalties at six and twelve months.
The deadlines
These apply to the 2026/27 tax year, which ran from 6 April 2026 to 5 April 2027.
| Deadline | What is due |
|---|---|
| 5 October 2027 | Register for Self Assessment if this is your first return |
| 31 October 2027 | Paper tax returns |
| 30 December 2027 | Online return, if you want tax collected through your PAYE code |
| 31 January 2028 | Online return, balancing payment and first payment on account |
| 31 July 2028 | Second payment on account |
What late filing costs
Penalties stack. They are charged even if you owe no tax at all.
| How late | Penalty |
|---|---|
| 1 day | £100, automatic |
| 3 months | £10 a day, up to £900 |
| 6 months | A further £300 or 5% of the tax due, whichever is higher |
| 12 months | Another £300 or 5%, and up to 100% in serious cases |
A return twelve months late with no tax owed still costs £1,600 in penalties. The £100 is not the end of it.
Late payment is charged separately
Paying late attracts its own penalties: 5% of the unpaid tax at 30 days, another 5% at six months and another 5% at twelve months, plus interest running throughout at the Bank of England base rate plus 2.5%.
If you cannot pay, set up a Time to Pay arrangement with HMRC before the deadline rather than after. Doing so stops the late payment penalties, though interest still runs.
Payments on account catch people out
If your tax bill is over £1,000 and less than 80% of your income is taxed at source, HMRC asks for payments on account towards next year, each half of this year’s bill.
That means your first January can be a shock: the balance for last year plus 50% of it again on account. A £4,000 bill becomes £6,000 payable in January and another £2,000 in July.
Reasonable excuse appeals
You can appeal a penalty within 30 days if you had a reasonable excuse: serious illness, a bereavement, a fire or flood, a genuine HMRC service failure, or unexpected hospital treatment.
Not accepted: finding the system too difficult, failing to get a reminder, relying on someone else who let you down, or not having the money.
This guide is general information, current at 9 November 2026. Tax rules change and depend on your circumstances. Please take advice before acting on it.