Self Assessment late penalty calculator

Self Assessment penalties at a glance

Plus late payment interest at 7.75% a year (from 9 January 2026) on tax paid late. Standard penalties for the 2025-26 return. Source: GOV.UK.

Worked examples

Two weeks late. You file and pay a £2,000 bill on 15 February 2027. You get the £100 filing penalty and about £6.37 interest (15 days at 7.75%). No late payment penalty, because you paid within 30 days.

Six weeks late. You file and pay £5,000 on 15 March 2027. That's £100 for filing late, £250 (5%) for paying after 2 March, and about £45.65 interest: £395.65.

Seven months late. You file and pay £10,000 on 31 August 2027. Filing: £100 + £900 daily penalties + £500 (5%, more than £300) at 6 months = £1,500. Payment: 5% at 30 days and 5% at 6 months = £1,000. Interest for 212 days is about £450.14. Total about £2,950.

No tax to pay. You owe nothing but file on 10 June 2027. You still pay £100 plus 41 days of daily penalties (£410): £510.

How Self Assessment penalties work

There are two separate deadlines on 31 January 2027 for the 2025-26 tax year (6 April 2025 to 5 April 2026): one for sending your tax return online and one for paying the tax you owe. Miss either and HMRC charges penalties. Paper returns had an earlier deadline of 31 October 2026, so if you missed that, file online instead: the online deadline still applies to you.

Filing late

The first penalty is a flat £100 the day after the deadline. It applies even if you owe no tax or have already paid. If the return is still missing 3 months later, HMRC can charge £10 a day for up to 90 days, so up to £900 more. At 6 months there's another penalty of 5% of the tax due or £300, whichever is bigger, and the same again at 12 months.

Paying late

Late payment penalties are separate. If tax is still unpaid 30 days after the deadline, HMRC adds 5% of the unpaid amount, then another 5% at 6 months and another at 12 months. For the 31 January 2027 deadline, HMRC's manual puts the first penalty date at 3 March 2027, so paying in full by 2 March avoids it. These penalties apply to the balancing payment, not to payments on account. Interest is charged on top, on everything paid late (including the first payment on account for 2026-27), from the day after it was due. The rate is the Bank of England base rate plus 4%: 7.75% from 9 January 2026, checked on GOV.UK on 22 October 2026.

What about the new points-based penalties?

Making Tax Digital for Income Tax brings new penalties: points for late returns, a £200 fine at the threshold, and late payment penalties that grow the longer you leave it. GOV.UK says the current penalties still apply to your 2025-26 return due on 31 January 2027, even if you joined Making Tax Digital in April 2026. The new rules apply from the year you join (2026-27 onwards for most people) and, from April 2027, to everyone who sends a personal Self Assessment return. The exception is people who volunteered early and agreed to the new penalties. If that's you, HMRC will have written to confirm it, and you can pick that option in the calculator above.

If you can't file or pay on time

File on time even if you can't pay: the filing penalties are often the bigger cost, and you need the return in to know your bill. If you can't pay, contact HMRC about a payment plan as early as you can. HMRC's manual says that if they agree to let you pay later before the payment is due, you won't get late payment penalties on that amount as long as you stick to the agreement. Interest still runs.

If something outside your control stopped you, you can appeal. GOV.UK's examples of a reasonable excuse include a close relative dying shortly before the deadline, an unexpected stay in hospital, a serious illness, a computer or HMRC system failure, and fire, flood or theft. Not having the money, finding the system hard or not getting a reminder don't count. You usually have 30 days from the date of the penalty notice to appeal, and you must file or pay as soon as you're able to.

To avoid all of this next time, put money aside through the year: the tax set-aside calculator and our guide to how much tax to set aside show you how, and the payments on account calculator shows what's due on 31 January and 31 July.

Frequently asked questions

What is the penalty for filing a Self Assessment tax return late?
If your online return for 2025-26 isn't in by 31 January 2027, you get a £100 penalty, even if you owe no tax or pay on time. After 3 months HMRC can add £10 a day for up to 90 days (£900). At 6 months there's a further penalty of 5% of the tax due or £300, whichever is more, and the same again at 12 months.

What is the penalty for paying Self Assessment tax late?
Under the current rules, 5% of the tax still unpaid 30 days after the deadline, another 5% of whatever is still unpaid at 6 months and another 5% at 12 months. For a 31 January 2027 deadline, HMRC's penalty date is 3 March 2027, so paying in full by 2 March avoids the first 5%. Interest is charged on top from the day after the deadline.

Do the new points-based penalties apply to my 2025-26 tax return?
Almost certainly not. GOV.UK says the current penalties apply to the 2025-26 return due on 31 January 2027, even if you started Making Tax Digital for Income Tax in April 2026. The new points-based late submission penalties and the new late payment penalties apply from the year you join Making Tax Digital (2026-27 onwards for most people), and from April 2027 to everyone who files a personal tax return. The only exception is people who volunteered for Making Tax Digital early and agreed to the new penalties; HMRC writes to confirm when they apply.

How much interest does HMRC charge on late Self Assessment tax?
Late payment interest is the Bank of England base rate plus 4%. GOV.UK lists it as 7.75% from 9 January 2026 (checked 22 October 2026). It's charged on tax you pay late, including late payments on account, from the day after it was due until you pay, and the rate changes when the base rate does.

Do I get a penalty if I owe no tax?
Yes, for a late return. The £100 penalty and the daily penalties don't depend on how much tax you owe, and the 6 and 12-month penalties are at least £300 each. If you don't think you need to file a return at all, contact HMRC before the deadline: if they agree to cancel the request, late filing penalties already charged are cancelled too.

Can I appeal a Self Assessment penalty?
Yes, if you have a reasonable excuse, such as a serious illness, a close relative dying shortly before the deadline, or a failure in HMRC's online services. You usually have 30 days from the date of the penalty notice to appeal. Not having the money, finding the system hard to use or not getting a reminder don't count. Send your return or payment as soon as you can.

What if I can't pay my tax bill by 31 January?
File your return on time anyway, so you avoid the late filing penalties, then contact HMRC about a payment plan. HMRC's manual says that if they agree to let you pay later before the payment is due, you don't get late payment penalties on that amount as long as you keep to the agreement. Interest is still charged.

Never get caught out again

The UK Self Assessment Tax Set-Aside & Payments-on-Account Planner turns your income into a monthly set-aside, tracks what you've saved, works out payments on account and lists your payment dates. It's available now in the Straight Sums shop for £7.

Add 31 January and 31 July to your calendar with the free UK tax deadlines calendar, read the payments on account guide, and check whether Making Tax Digital for Income Tax applies to you from April 2026, 2027 or 2028.

Sources

GOV.UK: Self Assessment tax returns: penalties, Self Assessment tax returns: deadlines, HMRC interest rates for late and early payments, Penalties for Making Tax Digital for Income Tax volunteers, Penalties for Making Tax Digital for Income Tax, Reasonable excuses, Disagree with a tax decision or penalty, If you cannot pay your tax bill on time, HMRC's own penalty estimator, HMRC manual CH62080 (late filing penalties), CH62120 (daily penalties), CH62140 (6-month penalty), CH155010 (late payment penalties), CH155180 (late payment example). All checked on 22 October 2026. General guidance and estimates only, not tax or financial advice. If anything here differs from GOV.UK or a letter from HMRC, they are right.