When is the self-assessment tax return deadline?

The self-assessment deadline is fast approaching with millions being urged to act. On 5 January, HMRC estimated around 5.85 million people were still yet to submit their tax returns for the 2024/25 tax year.

While the process of filing a tax return return can be a chore, it is very important that you do it – and that you do it on time – otherwise you risk incurring a penalty.

If you have received earnings of over £1,000 in the last tax year from any type of income outside of PAYE, you will need to complete a self-assessment tax return. This income could come from you being self-employed, being a buy-to-let landlord, or investments held outside of a stocks and shares ISA.

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You may also need to file a tax return if you need to pay back Child Benefit and can’t do it through PAYE.

You may need to complete self-assessment even if you don’t owe HMRC any tax.

If you need to file a self-assessment tax return and have not done it yet, then two deadlines have already passed – and the most important one is fast approaching.

Failure to submit your self-assessment on time means you could face paying a penalty of hundreds or even thousands of pounds depending on how late you are – and you could also have to pay 7.75% interest on top.

Alice Haine, personal finance analyst at Bestinvest, said: “Putting personal finance admin on the backburner is something many of us are guilty of, but leaving your self-assessment tax return until the final days of January puts you at risk of missing the deadline and receiving a fine.

“A tax return can require detailed information and time to ensure everything is correct. Leave it too late, however, and you risk missing the online submission deadline at midnight on January 31, and incurring an instant fine, with additional penalties the longer the return or any tax owed remains outstanding.”

Here is everything you need to know about self-assessment, and the deadlines you need to watch out for.

When is the self-assessment tax return deadline?

There are two main deadlines for filing a self-assessment tax return for the 2024/25 tax year, depending on how you do it.

The majority of people in the UK file their tax returns online, and the deadline to complete this is 23:59 on 31 January 2026.

Some people prefer to fill out a paper tax return. The deadline to do this for the 2024/25 tax year was 31 October 2025, which has already passed. If you were planning to do a paper tax return but missed the deadline, you will now have to complete self-assessment online.

The January deadline is not only when you need to file your return, but also when you need to pay any outstanding income tax – regardless of whether you file a paper or online return.

Some taxpayers also need to make payments on account. You will need to make the first payment for this by 31 January 2026, with a second payment deadline on 31 July 2026.

If you haven’t done a self-assessment tax return before but need to do one for the 2024/25 tax year, the deadline to register has already passed. It was 5 October 2025.

If you missed that deadline, and registered after 5 October, HMRC will send you a letter or email with a different deadline to file your tax return by – three months from the date on the letter or email.

The deadline has also passed for those who want to pay your tax bill through an automatic adjustment to your PAYE tax code. You would have had to submit your online tax return by midnight on 30 December 2025.

To pay tax through your PAYE tax code, you have to owe less than £3,000 in income tax from self-employment and must be currently employed or receiving a company pension.

What happens if I miss the self-assessment tax return deadline?

If you miss the self-assessment tax return deadline, you will have to pay a penalty to HMRC. The size of this penalty depends on how late you are and why you filed your tax return late.

One day late

There is a flat £100 fine for filing the return late, even if only by one day.

Three months late

After three months (so if you file an online tax return, that means from 1 May), you get hit with additional daily penalties of £10, up to a maximum of £900.

Six months late

After six months, a further penalty applies – either 5% of the tax due or £300, whichever is greater.

12 months late

The same fine (5% or £300) applies again once you are 12 months late.

You can also be hit with a penalty if you pay your tax bill late, including 5% of any unpaid tax at 30 days, six months and 12 months. Interest is also charged on top.

Self-assessment is payable via gov.uk or you can download the HMRC app and pay that way.

Some people put off dealing with their paperwork because they can’t afford to pay their tax bill – but this is a bad idea.

Alastair Douglas, chief executive at financial services company TotallyMoney, said: “If you’re struggling to pay your bill in full, then head over to the HMRC website where you might be able to set up a payment plan under a ‘Time to Pay’ arrangement.”

What happens if I make a mistake with my tax return?

If you make a mistake with your tax return, you can correct it even after the deadline. Tax return mistakes can be corrected within 12 months of the tax return being filed, with a new tax bill due on the updated return.

You will need to wait at least 72 hours after filing your return to make any changes.

How do payments on account work?

Payments on account are advance payments you make towards your next tax bill, ahead of the 31 January 2026 deadline.

They are designed to help you spread the cost of your tax rather than having to pay it in one go.

There are two payments on account due, each of which is around half of the previous year’s tax bill. Once you file your tax return, you can then determine whether a top-up payment is needed in order to clear the amount owed, or whether you can claim a refund.

The first payment on account must be paid by 31 January 2026, while the second must be paid by 31 July 2026.

So for example, if your tax bill for 2023/24 was £20,000, you will be required to make two payments on account, worth £10,000 each, for the 2024/25 tax year, with those payments required by 31 January and 31 July.

If you believe your tax bill is likely to be lower than the previous tax year, you can apply to have your payments on account reduced.

You can do this by signing into your online account via gov.uk and selecting the option to “reduce payments on account”.

How to hit the tax return deadline on time and avoid overpaying

There are certain things to bear in mind if you want to remove the stress involved with filing a self-assessment tax return correctly and on time.

First and foremost, it’s a really good idea to give yourself as much time as possible.

Registering to file a tax return can take a while, since you’re relying on the postal service to send you a Unique Taxpayer Reference (UTR) number. The earlier you start this process, the better.

Similarly it’s crucial you take the time to gather together all the relevant paperwork before you start attempting to fill in the return. That means bringing together your payslips, details of other income sources, savings and investments, pension contributions and charitable donations.

Zena Hanks, partner in the private wealth team at accountancy firm Saffery, added: "Being organised is half the battle: gather all relevant paperwork, including P60s, P11Ds or P45s, and don’t forget to declare investment income, dividend payments or any asset sales liable for capital gains tax."

Understanding the tax allowances and tax reliefs that apply to you means you may be able to reduce the actual tax you have to pay.

This can include the working from home allowance, the uniform allowance and the trading allowance of up to £1,000 for casual income.

Once you’ve got that information together, it’s important to double-check the calculations and make sure everything is accurate before you submit. Even if you make errors in good faith, you may be charged penalties by HMRC.

When the submission is finished, it’s useful to take lessons from it to work out how to reduce your tax bill in future years. In particular, topping up your pension can lower your tax liability, as well as help provide for your retirement.

You should also keep an eye on any changes to your tax code and check that it remains accurate for your circumstances.

Who needs to file a self-assessment tax return?

If your only source of income is your salary and you are not self-employed, then you probably don’t need to file a tax return. Your income tax will be deducted from your salary before you receive it through PAYE (which stands for “pay as you earn”).

Pension income is generally taxed through PAYE too, if you exceed the personal allowance.

However, if you also earn income from savings and investments held outside an ISA, a business, a second home, or another source, then it is likely you will need to file a tax return. The same is true if you are self-employed.

In recent years, more people have found themselves being dragged into the self-assessment net thanks to the effects of fiscal drag. This is because inflation has been high, but tax thresholds have remained frozen. As a result, the tax-free allowances are worth less than they once were in real terms.

If you’re unsure whether you need to file a tax return, HMRC’s online tool helps you check.