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.
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.
If HMRC issues these fines, you may be able to appeal them if you have a reasonable excuse for being late.
But there are a number of genuine excuses that HMRC may accept if you appeal a late fine, which include:
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.
If you're still yet to file your tax return, it's best to get your figures to HMRC as soon as possible.