Self Assessment Penalties: What You Owe at 1 Day, 3 Months, 6 Months and a Year

Miss the online self assessment deadline by one day and you owe HMRC £100. Leave the same return unfiled and unpaid for a year on a £9,000 tax bill and you owe £3,250 in penalties plus roughly £700 in interest, on top of the tax. The reason the number climbs so fast is the thing most people never realise: late filing and late payment are two completely separate penalty ladders, and they run at the same time, on the same bill.

HMRC said an estimated 1.1 million customers missed the 31 January deadline for the 2022 to 2023 return, against 11,581,962 returns filed on time. That is roughly one in eleven. Most of them will have paid the £100 and assumed that was the end of it. It is not, and this guide walks the whole thing rung by rung.

The two ladders, side by side

Read this table across, not down. The left column is what you pay for the return being late. The right column is what you pay for the money being late. They are charged independently, so a return that is twelve months late on tax that is also twelve months late collects from both columns.

All of the figures above come straight from HMRC's self assessment penalties guidance on GOV.UK. If you want the running total for your own dates rather than the ladder in the abstract, put them into the self assessment penalty calculator.

The late filing ladder in detail

The first £100 is a flat charge. It is not a percentage of anything, it does not scale with your bill, and it does not care whether you owe tax at all. One minute past 11:59pm on 31 January and it is issued.

Once the return is three months late, HMRC can add daily penalties of £10 a day. These are capped at £900, which is 90 days' worth, so they stop growing when the return is about six months late. That £900 is the single biggest jump on the filing ladder and it is the one people are least prepared for, because it accrues quietly while nothing arrives in the post.

At six months late there is a further penalty of 5% of the tax due or £300, whichever is greater. At twelve months, another 5% or £300 on the same greater-of basis. Those three words, "whichever is greater", are why a nil return is not a free pass, and we will come back to that.

Partnerships are hit harder than most people expect. HMRC's rule is that all partners will be charged a penalty if a partnership tax return is late. Not just the nominated partner. All of them. A four-partner firm that is a year late is looking at the full filing ladder four times over.

The late payment ladder in detail

This one is pure percentage. You get penalties of 5% of the tax unpaid at 30 days, at 6 months and at 12 months. Each one is calculated on what is still outstanding on that date, so paying something down between rungs genuinely reduces the next penalty.

Two things make this ladder catch people out. First, it starts at 30 days, not at three months, so it bites earlier than the daily filing penalties do. Second, it applies to your balancing payment and to any payments on account that fall due on 31 January. If you did not budget for the payment on account, that is the amount most likely to sit unpaid past the 30-day mark. Work out what yours should be with the payments on account calculator before January rather than after.

Interest: the meter that never stops

Interest is not a penalty and it is not capped. It runs on unpaid tax, and it runs on unpaid penalties too, which must themselves be paid within 30 days of the date on the penalty notice.

The formula is set in law rather than picked each year. Since 6 April 2025, HMRC late payment interest has been the Bank of England base rate plus 4 percentage points. It was base rate plus 2.5 points on or before 5 April 2025. Repayment interest, which is what HMRC pays you when it has held your money, is base rate minus 1 point with a floor of 0.5%.

The most recent rate published on HMRC's rate table when this guide was written was 7.75% for late payment, in force from 9 January 2026, with repayment interest at 2.75%. Rates move whenever the base rate moves, so check the current figure on the HMRC interest rates page before you rely on a number. To see what a specific delay costs at a specific rate, use the late payment interest calculator.

Worked example: Daniel does nothing for a year

Daniel is self-employed. His 2025 to 2026 return was due online by 11:59pm on 31 January 2027, with £9,000 of tax due the same night. He files nothing and pays nothing until February 2028.

• 1 February 2027 — £100 filing penalty. Interest starts running on the £9,000.
• 2 March 2027, 30 days late — first late payment penalty, 5% of £9,000 = £450.
• 1 May 2027, 3 months late — daily penalties begin at £10 a day, reaching the £900 cap by the end of July.
• 1 August 2027, 6 months late — filing penalty of 5% of £9,000 = £450, which beats the £300 floor. Second late payment penalty, another £450.
• 1 February 2028, 12 months late — filing penalty of another £450. Third late payment penalty, another £450.

Filing penalties: £100 + £900 + £450 + £450 = £1,900. Payment penalties: £450 + £450 + £450 = £1,350. That is £3,250 of penalties on a £9,000 bill, before interest. A full year at 7.75% on £9,000 adds roughly £700. Daniel's £9,000 has become about £12,950.

Notice that £1,900 of that, the entire left-hand column, would have disappeared if he had filed a return with estimated figures on 31 January 2027 and amended it later.

The trap: on time to file, late to pay

Ruth files her 2025 to 2026 return on 20 January 2027, eleven days early, and feels organised. Her bill is £4,800. A client pays her late, so the money does not reach HMRC until 20 April 2027.

Her filing penalties are zero. She did everything right on that ladder. But the tax was 30 days late on 2 March 2027, so she gets a late payment penalty of 5% of £4,800 = £240. Interest at 7.75% on £4,800 for the 79 days from 1 February to 20 April adds roughly £80. Filing early bought her nothing at all on the payment side. She pays about £5,120.

This is the most common misunderstanding in self assessment. "I filed on time" is a complete defence against one ladder and no defence whatsoever against the other. If you know the money will be short, the fix is not to delay the return. It is to file, then talk to HMRC about instalments.

The nil return trap

Marcus wound down a small side business in 2024 but never told HMRC he no longer needed to file. A notice to file for 2025 to 2026 arrives and he bins it, reasoning that he owes nothing so there is nothing to penalise.

Thirteen months later his position is £100, plus £900 of daily penalties, plus £300 at six months and £300 at twelve months, because the tax-geared penalties are 5% of the tax due or £300, whichever is greater, and 5% of nothing is nothing. That is £1,600 of penalties on a nil tax bill. There are no late payment penalties and no interest, because there is no tax. The filing ladder does not care.

Once HMRC has issued a notice to file, the obligation exists until HMRC withdraws it. If you genuinely no longer need to file, you close your self assessment account through your HMRC online account, and HMRC needs time to review that request before the 31 January deadline. Leave it too late and you may still get a penalty. If you are unsure whether you are still in the system, the do I need to file a self assessment checker is the quickest way to work it out, and the rules on registering by 5 October matter in the other direction, because registering late brings a separate failure to notify penalty.

What actually counts as a reasonable excuse

A penalty can be cancelled if you had a reasonable excuse and you put things right as soon as the excuse ended. HMRC lists examples that may qualify: the death of your partner or another close relative shortly before the deadline, an unexpected stay in hospital that stopped you dealing with your tax affairs, a serious or life-threatening illness, your computer or software failing while you were preparing your online return, problems with HMRC's own online services, a fire, flood or theft, postal delays you could not have predicted, delays related to a disability or mental illness, being unaware of or misunderstanding your legal obligation, and relying on someone else to send your return who then failed to do so.

HMRC is just as clear about what does not count. A cheque that bounced or a payment that failed because you did not have enough money is not a reasonable excuse. Finding the HMRC online system too difficult to use is not. Not getting a reminder from HMRC is not. Making a mistake on your tax return is not.

Read the current list on GOV.UK's reasonable excuses page before you write anything. The pattern is that HMRC accepts things that happened to you and rejects things that were within your control. "I was busy" is within your control. "I was in hospital" is not.

How to appeal, and the 30-day clock

You usually have 30 days from the date your penalty was issued to contact HMRC or make an appeal. Miss that and you will need to give a reason for being late with the appeal as well as a reason for the original failure, which is two arguments instead of one.

Check the penalty letter first, because it tells you how to appeal and often comes with the right form. If no form came with it, a signed letter to the HMRC office named on the notice works. Keep it short and factual: the penalty reference, the dates, what happened, when it ended, and the date you filed or paid once it did. Attach evidence, and file the outstanding return before or alongside the appeal, because HMRC will not usually cancel a filing penalty while the return is still missing.

If you cannot pay the tax

Filing is free. Paying is the hard part, and the worst thing you can do is go quiet. HMRC can agree a Time to Pay arrangement letting you settle in instalments, and there is an online service that checks whether you are eligible and sets one up without a phone call. You will need your tax reference, UK bank details for a Direct Debit, and figures for your income and spending. Start at GOV.UK's guidance on what to do if you cannot pay your tax bill on time.

Interest keeps running on anything covered by an instalment plan, so a plan reduces the pain rather than removing it. It is still far better than the alternative, because the 5% payment penalties are charged on tax still unpaid at 30 days, 6 months and 12 months whether you have been ignoring HMRC or simply cannot find the money.

The dates that stop any of this happening

For the 2025 to 2026 tax year, which ended on 5 April 2026, the dates are fixed.

Those dates are confirmed on the GOV.UK self assessment deadlines page. If your figures are not ready by 31 January, file with your best estimate, flag the figures as provisional, and amend the return later. An estimate might cost you a little interest. Silence costs you £100 immediately and up to £1,900 within a year.

For the wider picture on what has to be reported and when, our guides to self assessment deadlines and how to file and self-employed tax for beginners cover the return itself, and the £1,000 trading allowance explains when a side income does not need a return at all.