Self Assessment Deadlines: Every Date You Need and What Happens If You're Late

The deadlines at a glance

HMRC must receive your tax return and any money you owe by the deadline. For the tax year that ran from 6 April 2025 to 5 April 2026, the deadlines are confirmed on GOV.UK as follows.

5 October: tell HMRC you need to file

You must tell HMRC by 5 October if you need to complete a return for the previous tax year and either you've never sent one before, or you registered before but didn't send a return for 2024/25. Registering for Self Assessment is done online on GOV.UK, and our Self Assessment timeline guide walks through registration, the activation code and each date in order.

If you register after 5 October 2026, HMRC will write to you with a different filing deadline: three months from the date on their letter or email. That flexibility doesn't extend the bill. You still have to pay any tax you owe by 11:59pm on 31 January 2027, and registering late can lead to a 'failure to notify' penalty if tax is left unpaid.

31 October: paper returns

If you'd rather post your return, HMRC must receive it by 11:59pm on 31 October 2026. Paper returns can be sent any time from 6 April onwards, so there's nothing to gain from waiting until the autumn. A handful of filers, including trustees of registered pension schemes and non-resident companies, must use paper and get until 31 January 2027.

31 January: online returns and payment

Most people file online, and the deadline is 11:59pm on 31 January 2027. The same date covers the balancing payment, and the first of two payments on account if HMRC has asked you to make them.

One earlier date matters if you pay tax through your salary: if you owe less than £3,000 and want it collected through your PAYE tax code, you must submit the online return by 11:59pm on 30 December 2026. Miss it and the whole bill is payable by 31 January. Our guide to payments on account explains when the 31 January and 31 July instalments apply.

What a late return costs

The late filing penalties are fixed amounts and time-based, and they apply even if your return shows no tax due.

Paying late is charged separately

On top of filing penalties, paying late brings its own charges: 5% of the tax still unpaid at 30 days, another 5% at 6 months and a further 5% at 12 months, plus interest on the amount owed. A return sent a day late has already cost £100; one left for a year can cost several hundred pounds before a penny of tax is counted.

Can you appeal a penalty?

Yes, if you had a reasonable excuse. HMRC accepts appeals where something outside your control stopped you filing or paying on time, and you can appeal online on GOV.UK. If the excuse is accepted, the penalty is cancelled; if not, you still have to pay it within 30 days of the penalty notice.

Beat the deadline

You can submit from 6 April onwards, and filing early means you know the bill months before it's due. Work out what you'll owe with the Self Assessment tax calculator, or see how to complete a Self Assessment return step by step. Our tax year planner lists the other dates worth diarising, and if you're new to self-employment the self-employed tax guide covers National Insurance and expenses too.