Self Assessment deadline and late penalty calculator, 2025/26

The paper and online return deadlines are different, but the date you must pay by is 31 January 2027 whichever way you file. A paper return filed in November 2026 is late, while an online return filed on the same day is not. GOV.UK: Self Assessment tax returns deadlines.

Interest is charged on top of late-payment penalties. GOV.UK does not spell out the day-by-day counting, but Schedule 55 of the Finance Act 2009 does: the penalty date is the day after the filing deadline, and the late-filing penalties apply if the return is still outstanding after the end of the 3, 6 and 12 month periods beginning with that date (for an online 2025/26 return that is 1 May, 1 August and 1 February). A return filed on one of those start dates does reach it, because the failure then continued after the end of the period (Schedule 55, paragraphs 4 to 6). Our own assumptions, which HMRC's notices may treat differently: the daily penalties are counted for each day from the start date to the day you file, up to 90 days, although HMRC must send a notice for them and the calculator assumes it does; and the late-payment points follow Schedule 56 of the Finance Act 2009: the first 5% applies if tax is unpaid after 30 days from the payment deadline (2 March 2027 for 2025/26), the penalty date is the next day, and the further 5% charges apply if it is still unpaid after the 5 and 11 month periods beginning with that date. Those periods end on 2 August 2027 and 2 February 2028, so paying on those days is the last penalty-free day for that charge and paying the next day (3 August 2027 or 3 February 2028) incurs it. That is a day or two later than counting a flat 6 and 12 months from 31 January. HMRC confirms the exact amount in its notices, and can cancel a penalty if you have a reasonable excuse. GOV.UK: Self Assessment penalties; Finance Act 2009, Schedule 55; GOV.UK: appeal a tax penalty.

Late filing: £100 once the deadline has passed, then £10 for each day from 3 months after the penalty date, capped at £900 (90 days), then the greater of 5% of the tax due or £300 at 6 months and again at 12 months. Late payment: 5% of the unpaid tax at 30 days, 6 months and 12 months. The calculator shows the headline amounts quoted by GOV.UK; it does not apply HMRC's special cases, such as caps where a penalty would exceed the tax due, or a reasonable excuse, and it does not calculate interest.

Example: an online 2025/26 return filed on 1 June 2027 with £2,000 of tax paid on time is £100 plus 32 daily penalties (1 May to 1 June) of £10, which is £420. Late payment penalties would be extra if the £2,000 had not been paid.

Checked 29 October 2026. Sources: GOV.UK, Self Assessment tax returns deadlines; GOV.UK, Self Assessment penalties. General information, not tax advice: HMRC's notices decide what you owe.