The deadline for online tax returns is 23:59 today so Friday 31 January is the last chance to fill in the form and get it straight back to HMRC.

With changes to Making Tax Digital for income tax self assessment due to start in April 2026, those who really hate doing a tax return might prefer to do quarterly reporting, although the added red tape is questionable.

HMRC issues penalties automatically so be warned, while HMRC charges base rate plus interest on late payments, so expect to pay 7.5% for any overdue payments, and this is going to rise with an extra levy of 1.5% on the base rate to an eye watering 9% from April.

 Zena Hanks, partner in the Private Wealth team at Saffery LLP, said: ‘The incentives to file returns on time continue to mount up. Late payment interest rates are already enough to make people wince – given they are linked to the Bank of England base rate which remains higher than normal, plus 2.5%.

‘The government has confirmed that it will be adding a further 1.5% interest rate rise on late payments, estimated to rake in more than £250m for the Treasury from April.

‘The potential hit of a late payment penalty is something to be reckoned with this self-assessment season and taxpayers should do everything in their power to ensure they file and pay on time each year, so they do not contribute to these eye-watering penalty figures.’

But it is important to realise that there can be extenuating circumstances which make it difficult to meet the filing deadline, and in some cases HMRC will accept a late filing excuse. However, the rules are complex and care must be taken.

Chris Etherington, partner at RSM, said: ‘What classifies as reasonable is not always well understood. Individuals suffering from an illness or a mental health condition may have grounds for an appeal against a late filing penalty.

‘A taxpayer making a reasonable excuse will need to show they have taken reasonable care in trying to meet their obligations. Part of the test involves imagining what someone similar to you might have done in the same circumstances if they wanted to meet the deadline.’

According to HMRC online information, a reasonable excuse is defined as ‘something that stopped you meeting a tax obligation for a valid reason’.

Etherington added: ‘HMRC will consider each individual’s circumstances on their own merits and the comparison to a hypothetical person will be with someone standing in the same shoes.

‘However, HMRC’s guidance indicates that simply asserting that you are suffering from a mental health condition is unlikely to be sufficient. A taxpayer will also need to demonstrate how their condition “detrimentally affected their ability to comply with their tax obligation”.’