If you miss 31 January, this is what happens
Around a million returns arrive late every year. The penalties are automatic, they are the same whether you owe £5 or £5,000, and they are worst for people who go quiet. Here is the sequence for the 2025/26 return, due 31 January 2027.
Late return
Left for a year, a return with no tax to pay at all has cost £1,600. That is the part people find hardest to believe.
- 1 February 2027: a £100 penalty, even if you owe no tax or are due a refund.
- From 1 May 2027, three months late: £10 a day for up to 90 days, so up to £900 on top.
- 1 August 2027, six months late: a further £300, or 5 percent of the tax due if that is more.
- 1 February 2028, twelve months late: another £300 or 5 percent. In serious cases HMRC can charge up to 100 percent of the tax.
Late tax
These run separately, on the tax itself. Interest is charged from 1 February 2027 on anything unpaid, at the Bank of England base rate plus 4 points. Then a 5 percent penalty on the tax still unpaid after 30 days, another 5 percent after six months, and another after twelve.
The one thing that stops it growing
File. The daily penalties and the six and twelve month penalties are all about the return, not the payment. A return filed in March with the tax unpaid stops the clock on every penalty in the first list. You then owe the £100, the tax, and interest, and you can ask HMRC for time to pay the tax in instalments, which they usually agree to online for amounts under £30,000.
If you cannot pay, file anyway. If you do not have every figure, file your best estimate, tick the box that says so, and correct it later. An estimated return on time beats an exact return in April.
Reasonable excuse
HMRC cancels penalties for a reasonable excuse: a serious illness, a bereavement close to the deadline, a fire or flood, HMRC’s own systems being down. Being busy, not knowing the rules, finding the form difficult or waiting on an accountant do not count. You appeal within 30 days of the penalty notice, and the appeal is easier if the return has since been filed.
What it costs you, in numbers
The calculator below takes the date you expect to file, the date you expect to pay and the tax due, and gives the penalties and interest as a figure. Use it before the deadline rather than after, because the answer is usually enough to get the return done.
Figures are for the 2025/26 tax year and were checked against gov.uk on 16 October 2026. This is general information, not advice about your own position.