What happens next if you’re one of them?

Around one million taxpayers missed the 31 January deadline for submitting their 2024/25 self-assessment tax return.

HMRC data shows just how last-minute things were for many people. More than 27,000 returns were filed in the final hour, with 475,722 submitted on the final day alone. In total, around 11.5 million returns were filed.

Even with extended helpline hours and webchat support, a significant number of people still didn’t make the deadline.

What happens if you miss it?

If you missed the deadline, the first thing to know is that a £100 fixed penalty is applied automatically.

This applies even if:

• You don’t owe any tax
• You’ve already paid what was due

From there, the penalties can increase quickly if the return remains outstanding.

How penalties build up

If your return is still not submitted:

• After 3 months: £10 per day (up to £900)
• After 6 months: £300 or 5% of the tax due (whichever is higher)
• After 12 months: another £300 or 5% charge

On top of that, late payment penalties may apply:

• 5% of unpaid tax after 30 days
• Another 5% after 6 months
• Another 5% after 12 months

Interest is also charged on any overdue amounts.

Who needs to file a self-assessment return?

Self-assessment generally applies if you have income that isn’t taxed automatically through PAYE.

That can include:

• Self-employment income over £1,000
• Rental income from property
• Other untaxed income streams

Can penalties be appealed?

HMRC has confirmed it will review cases where there is a reasonable excuse for missing the deadline.

However, in most cases, the practical advice is:

• Submit the return as soon as possible
• Pay any initial penalties promptly

Even if you plan to appeal, dealing with it early can prevent further charges from building up.

Final thoughts

Missing the deadline is more common than people think, but leaving it unresolved is where the real cost starts to build.

If you’ve missed the deadline or you’re not sure what to do next, it’s worth getting it sorted sooner rather than later.

If you need help with your self-assessment, I’m always happy to have a straightforward conversation.