Self-assessment deadline approaches - what to do if you can't pay

The deadline to file your online Self Assessment tax return and pay what you owe is 31 January 2026, covering the 2024/25 tax year. That’s for income earned between 6 April 2024 and 5 April 2025.

The paper deadline has already been and gone. It was on 31 October 2025. If you missed that, you’ll need to file online now.

What happens if you don’t file on time?

Miss the 31 January deadline and:

• you get an automatic £100 fine the very next day even if you don’t owe any tax
• after 3 months, daily fines kick in: £10 a day, up to £900
• after 6 months, you’re looking at another penalty of 5% of the tax due or £300, whichever’s higher
• after 12 months, HMRC can slap you with yet another penalty of the same amount, and in serious cases up to 100% of the tax owed

What happens if you file but don’t pay on time?

If you file your tax return on time but don’t pay what you owe, you’ll get penalties of 5% of the tax unpaid at the 30-day mark, 6 months’ mark and 12 months’ mark. HMRC charges interest at the Bank of England base rate plus 2.5%

What happens if you need to file a tax return but still haven’t registered for self-assessment?

The deadline to register for self-assessment for the 2024/2025 tax year was the 5th of October, 2025. Registering late can result in a penalty. However, this usually only happens if you register late and don’t pay what you owe by the deadline (31st January 2026 this year).

If you still haven’t registered, you should get started ASAP. You can find out more about registering for self-assessment on the government website.

It can take up to 15 days to get all the details you need to register depending on your circumstances. This means even if you get started immediately, you could still miss the deadline for filing and paying. But you’re better off registering now so you can avoid interest racking up on top of penalties.

What happens if you can’t afford to pay your bill?

If you know you can’t afford to pay your bill, you should still file your tax return to avoid late filing penalties.

You can also set up a payment plan which allows you to spread the cost. Sometimes, you can do this online. You’ll need:

• your tax reference number
• your UK bank account details
• details about your income and spending

HMRC will ask you to pay an amount based on how much you have left over after paying for essentials and some fixed outgoings. You can pay more though, which many people choose to do as interest continues to rack up if you choose to pay in instalments.

Deadlines for next year

If you want to get organised for next year’s tax return season, these are the main deadlines to keep in mind for the 2025/2026 tax year. This is for income earned between 6 April 2025 and 5 April 2026.

• 5 October 2026 – register for self-assessment if you haven’t already
• 31 October 2026 — paper return deadline
• 31 January 2027 — online return deadline

Key takeaways

• You must file your online tax return and pay your bill by 31 January 2026 for the 2024/25 tax year.
• Miss the filing deadline? Expect an automatic £100 fine, followed by daily penalties after 3 months and bigger penalties at 6 and 12 months.
• Filed but not paid? You’ll be charged interest and 5% late‑payment penalties at 30 days, 6 months and 12 months.
• Not registered yet? You should have registered by 5 October 2025, but if you didn’t, register ASAP as it can take up to 15 days to get set up.
• Can’t afford the bill? Still file your return, then set up a payment plan with HMRC to spread the cost and reduce extra charges.