Both parents and workers have just a few weeks left before an important deadline set by HM Revenue and Customs (HMRC) expires, with potential penalties of up to £1,600 for those who fail to meet it.

The tax authority has previously stated that anyone required to complete a Self Assessment must pay their outstanding tax by no later than 11.59pm on 31 January 2026. This deadline specifically applies to those submitting an online tax return, as opposed to a paper one, which should have been filed by 31 October of the previous year.

If you’ve missed the deadline for your paper returns, you’ll already be facing late filing penalties. A Self Assessment tax return is mandatory if you were categorised as a self-employed ‘sole trader’ earning more than £1,000 in the last tax year, needed to pay Capital Gains Tax when selling or disposing of something that increased in value, or were a partner in a business partnership.

You may also need to submit a return if you had to pay the High Income Child Benefit Charge and don’t pay it through PAYE, or have untaxed income, which can include foreign income, tips and commissions, and rental income from property. You can check whether you need to send a tax return here.

HMRC has encouraged taxpayers to utilise the HMRC app for settling their tax bills, highlighting its convenience and payment reminder features. Myrtle Lloyd, HMRC’s Chief Customer Officer, commented: “The Self Assessment deadline is less than one month away, and thousands of people have already paid their tax bill via the HMRC app.

“It is quick and easy to do, and you can also see your payment history. Search ‘download the HMRC app’ on GOV.UK to access the app and make your Self Assessment payment.”

A comprehensive list of payment methods for tax returns is available on GOV.UK here.

Penalties for missing the self-assessment deadline

HMRC regulations confirm that financial penalties can be imposed for any late tax returns. Initially, a fixed £100 fine is charged, which can escalate quickly if left unpaid.

Failure to submit your tax return within three months of the deadline results in daily penalties of £10, capping at £900. Beyond six months, the penalty increases to either 5% of the outstanding tax or £300, whichever sum is higher.

A further charge of 5% or £300, whichever is greater, is added after 12 months. HMRC emphasises that these penalties are entirely avoidable by submitting your Self Assessment tax return punctually.

Furthermore, people who fail to pay their tax on time will initially face a penalty of 5% of the unpaid tax, charged 30 days after the due date. This penalty will then escalate by an additional 5% if the payment is six months and 12 months overdue, respectively.

HMRC also highlights that interest will be applied to any outstanding tax owed.

What if you receive a penalty

If HMRC imposes a penalty for either a late tax return or a late payment, you may be able to evade paying it if you contest the decision. As per HMRC guidelines, having a ‘reasonable excuse’ is considered a valid reason for challenging the penalty.

Typically, you have a 30-day window from the date the penalty is issued to contact HMRC and officially file an appeal. If a deadline was missed, you will need to provide a justification for the delay.

The process for submitting an appeal will vary significantly depending on the type of tax you pay and whether you’re employed or self-employed. You can find comprehensive details here.