One Million Miss the Self Assessment Deadline: What to Do Next

HMRC has estimated that around one million taxpayers missed the 31 January 2026 Self Assessment deadline, despite 11.48 million people successfully filing on time.

As expected, there was a last-minute surge, with nearly half a million returns submitted on deadline day alone - and over 27,000 filed in the final hour before midnight.

However, for those who missed the deadline, it’s important to act quickly to minimise penalties.

Missed the deadline? Here’s what happens

If your return is still outstanding, HMRC applies an automatic £100 late filing penalty, even if no tax is due.

Further penalties increase over time:

• After 3 months: £10 per day (up to £900)

• After 6 months: 5% of the tax due or £300 (whichever is higher)

• After 12 months: an additional 5% or £300
  

In addition, late payment penalties apply to any unpaid tax, alongside interest charges.

What should you do now?

If you’ve missed the deadline, the priority is simple: file your return as soon as possible.

The sooner you act, the more you can limit further penalties and interest.

If you’re unsure where to start, or if your records aren’t up to date, getting professional support can help you resolve things quickly and correctly.

Looking ahead: Making Tax Digital is coming

There is also a significant change on the horizon.

From 6 April 2026, Making Tax Digital (MTD) for Income Tax will become mandatory for sole traders and landlords with income over £50,000.

Under MTD, you will need to:

• Keep digital records

• Submit quarterly updates to HMRC

• Complete an end-of-year submission
  

This represents a major shift in how tax reporting works and will require businesses to adapt their systems and processes.

Our view

Missing the deadline can happen - but the key is taking action quickly and putting the right processes in place for the future.

With MTD just around the corner, now is also a good time to review how you manage your records and reporting to avoid unnecessary stress going forward.

At SJC, Chartered Accountants we support clients with everything from catching up on late returns to preparing for MTD - ensuring you stay compliant and in control.|

If you need help filing your return or getting ready for Making Tax Digital, please get in touch.