Nearly one million missed the self-assessment deadline: what fines could you face?

A record 11.1 million people managed to submit their 2018-19 tax return on time, but 958,296 missed the crucial 31 January deadline.

Of the successful filers, a record 10.4 million submitted their return online, according to recent figures from HMRC.

However, plenty left it pretty late. More than 700,000 people waited until deadline day to submit their returns. Of those, more than 26,500 people left it until the eleventh hour, literally - completing their returns between 11pm to 11.59pm on the night of Friday 31 January.

If you haven't yet filed and paid your tax bill you need to act quickly to avoid penalties mounting up. Here, Which? explains what HMRC charges for late tax returns and payments and what could count as a reasonable excuse for filing late.

What late penalties could you face for missing the deadline?

The deadline for both tax returns and tax payments was 31 January, so many people who failed to submit their return could face additional fines for not paying their tax bill.

The penalties for both will increase the later you are, so it's best to get your return and payment to HMRC as quickly as possible.

For late tax returns:

• One day late: £100 fine
• Up to three months late: £10 for each additional day (capped at 90 days), plus initial £100 fine
• Six months late: either £300 or 5% of the tax due (whichever is higher), plus the penalties above
• 12 months late: all penalties above, plus another £300 or 5% of the tax due. In some cases, you can be fined up to 100% of the tax due.

For late tax payments:

• One day late: charged interest on what you owe (currently 3.25%)
• 30 days late: charge of 5% of the tax due
• Six months late: additional 5% charge
• 12 months late: additional 5% charge.

If HMRC issues these fines, you may be able to appeal them if you have a reasonable excuse for being late.

• Find out more:late tax returns and penalties for mistakes

Reasonable excuses for filing late

HMRC recently released a list of the weirdest excuses for filing a late tax return - for instance, your mother-in-law putting a curse on you is not going to work.

But there are a number of genuine excuses that HMRC may accept if you appeal a late fine, which include:

• the death of a partner or family member
• serious illness
• fire, flood or theft
• computer failure or issues with HMRC's online services.

There's a full list of reasonable excuses on the HMRC website, but each appeal will be decided on a case-by-case basis.

You'll also see a list of excuses that definitely won't be accepted, such as payment failing because you don't have enough money, or finding HMRC's system too difficult to use.

You can still file with Which?

If you're still yet to file your tax return, it's best to get your figures to HMRC as soon as possible.

Online tools such as the Which? tax calculator can help - it's easy to use and jargon-free, it can offer tips to make savings and you can submit the form directly to HMRC.

For more help and advice on filing your tax return, there's a host of Which? articles that can help, from tips for self-employed people to parents claiming child benefit, and things for landlords to be aware of.