What Happens If You Miss the Self Assessment Payment Deadline as a Sole Trader?

As a sole trader in the UK, you must complete a Self Assessment tax return each year if HM Revenue and Customs (HMRC) requires you to. This involves reporting your income and paying any tax you owe. The key deadline for paying your Self Assessment tax bill is 31 January following the end of the tax year (which runs from 6 April to 5 April).

Consequences of Missing the Payment Deadline

If you do not pay the tax you owe by 31 January, HMRC will charge you a penalty. A fixed penalty of £100 applies immediately after the deadline, even if you have no tax to pay or have paid some of it. Further penalties can apply if the payment remains outstanding:

After 30 days: an additional penalty of 5% of the tax due.
After 6 months: a further 5% penalty on any unpaid tax.
After 12 months: another 5% penalty on any unpaid tax.

In addition to penalties, HMRC charges interest on the unpaid tax from the day after the deadline until the tax is paid in full.

For example, if your tax bill for the 2025-2026 tax year is due by 31 January 2027 and you miss this deadline, you will face a £100 penalty from 1 February 2027, plus interest on the unpaid amount, and potentially further penalties if you continue to delay payment.

Payments on Account and Their Deadlines

If your previous Self Assessment tax bill was more than £1,000 and less than 80% of your tax was collected at source (e.g., through PAYE), you may need to make “payments on account” towards your next year’s tax. These are advance payments, usually due in two instalments:

31 January following the end of the tax year
31 July following the end of the tax year

Missing the 31 January payment deadline can lead to penalties on the amount overdue. To avoid further penalties, you must pay any outstanding balance plus the next payment on account by 31 July.

Late Filing Penalties Are Separate

It is important to distinguish between the payment deadline and the filing deadline for your tax return. You must file your tax return online by 31 January following the end of the tax year.

If you miss the filing deadline, you will face a separate fixed penalty of £100 immediately after the deadline, regardless of whether you owe tax. Additional penalties apply if the return remains outstanding after 3 months, 6 months, and 12 months.

What to Do If You Miss the Deadline

Pay the tax you owe as soon as possible to reduce interest and further penalties.
If you cannot pay in full, contact HMRC promptly to discuss payment options, such as a time to pay arrangement.
Keep records of your communications with HMRC.

HMRC may consider reasonable excuses for late payment or filing, but these are assessed on a case-by-case basis and do not guarantee that penalties will be waived.

Summary

Missing the Self Assessment payment deadline as a sole trader leads to a £100 fixed penalty, interest charges on the unpaid tax, and further penalties if payment is delayed. You must pay by 31 January following the tax year to avoid these charges. If you miss the deadline, paying as soon as possible and communicating with HMRC is essential. Remember that late filing of your tax return brings separate penalties, so meeting both deadlines is important to keep your tax affairs in order.

Official reference: https://www.gov.uk/self-assessment-tax-returns. Topic-specific official guidance. Always check the latest official guidance. Related forms: Browse our form category.

Important: This article provides general information. Government rules, forms and procedures can change, and this article may not reflect the latest updates. Check current GOV.UK guidance or the relevant authority before relying on it. ITG & Co. is independent and is not affiliated with a government department.