Self assessment deadlines 2027

The dates for your 2025/26 return

If you are reading this in November 2026, the first two dates have passed. That is fine for most people. If you have not registered yet, register now. The penalty for registering late is linked to tax that is still unpaid after 31 January, so filing and paying on time keeps it down. If you missed the paper deadline, file online instead. The online deadline is the one that counts.

Two payments land on 31 January

This is the part that catches people out. On 31 January 2027 you may need to pay two things at once:

• The balancing payment. Whatever you still owe for 2025/26, after any payments on account you already made.
• Your first payment on account for 2026/27. Half of your 2025/26 bill, paid in advance towards next year.

In your first year of self assessment there were no payments on account before, so the January bill can be 1.5 times the tax for the year. A sole trader with £32,000 of profit in 2025/26, in England, owes £5,051.80 of income tax and Class 4 National Insurance. Their 31 January 2027 bill would be:

Then another £2,525.90 is due by 31 July 2027. Our guide to payments on account walks through the rules, including when you do not have to make them.

Late filing penalties

If your 2025/26 return arrives after 31 January 2027, these penalties apply (from GOV.UK):

• an initial £100 penalty
• after 3 months, £10 a day, up to a maximum of £900
• after 6 months, a further 5% of the tax due or £300, whichever is greater
• after 12 months, another 5% or £300, whichever is greater

So a return that is a year late with a small bill can cost £100 + £900 + £300 + £300 = £1,600 in filing penalties alone.

Late payment penalties and interest

Paying late is a separate charge from filing late. If tax is still unpaid, you get a penalty of 5% of the unpaid tax at 30 days, at 6 months and at 12 months.

On top of that, HMRC charges interest on tax paid late. The late payment interest rate is 7.75% a year from 9 January 2026. It is set at the Bank of England base rate plus 4%, so it moves when the base rate moves. Check HMRC's interest rates page for the current figure.

The interest is small for a short delay. The 5% penalties are not. Paying even part of the bill on time reduces both.

If you cannot pay in full

File on time anyway. Filing late adds the £100 penalty and more, and you cannot know the exact bill until the return is done. Then pay what you can. If you cannot pay the full amount, you might be able to set up a payment plan with HMRC, known as a Time to Pay arrangement. GOV.UK explains it on the pay your Self Assessment tax bill page. For next year, a Budget Payment Plan lets you pay weekly or monthly by Direct Debit towards your next bill.

If you joined Making Tax Digital in 2026

People using Making Tax Digital for Income Tax from 6 April 2026 have a newer, points-based penalty system for 2026/27 onwards. Your 2025/26 return still uses the penalties above. See our Making Tax Digital guide for who it applies to and when.

A simple plan for the next few weeks

1. November: gather your 2025/26 income and expenses. Work out a rough profit and estimate the bill, including the payment on account.
2. December: file the return. You can file any time after 5 April. Filing early does not mean paying early. It just means you know the number.
3. January: pay by 31 January 2027. Put the July amount aside straight away.

Sole Sums does the first step for you and keeps a ready-to-file checklist. It does not file the return. You do that through your HMRC online account or recognised software.

Mistakes after you file

If you spot an error, you can correct your return within 12 months of the filing deadline. For 2025/26, that means by 31 January 2028. Online, you need to wait 3 days (72 hours) after filing before you can change it.