When is the self-assessment tax return deadline?

The first self-assessment tax return deadline of the 2025/26 tax year is fast approaching.

Anyone who needs to file a tax return because they have earned income from something other than PAYE (Pay As You Earn) work will need to meet this tax year’s deadlines or else face penalties.

Late filers are fined a flat £100 if they don’t complete their self-assessment in time and penalties increase the longer you take to submit your tax return.

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That’s why it’s always a good idea to start thinking about filing a self-assessment tax return early so you aren’t racing to get all your documents together days or hours before the deadline.

When is the self-assessment tax return deadline?

There are several deadlines you need to look out for when filing a self-assessment tax return for the 2025/26 tax year. The deadlines depend on how you will submit your return – such as by post or online.

The paper tax return deadline is the earliest of all, falling on 31 October, 2026.

The main online tax return deadline is 31 January 2027, three months after the paper deadline.

The January date is also the deadline for paying any income tax due for the 2025/26 tax year – regardless of which format of tax return you choose.

Some taxpayers also need to make their first payments on account by 31 January. We explain what this means in more detail below.

All tax return deadlines for the 2024/25 tax year have now passed.

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 (pay as you earn).

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

While many people associate self-assessment with the self-employed, it doesn’t just apply to that group.

If you earn income from savings and investments held outside an ISA, a business, second home or another source, you will likely need to file a tax return.

In recent years, more people have been dragged into the self-assessment net due to fiscal drag – inflation has been high but tax thresholds have remained frozen, meaning the tax-free allowances are worth less than in the past in real terms.

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

How do payments on account work?

Payments on account are advance payments you may need to make towards your next tax bill ahead of the 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 every tax year, each of which is around half of the previous year’s tax bill.

Once you file your tax return, you can determine whether a top-up payment is needed in order to clear the amount owed, or whether you can claim a refund.

For the 2026/27 tax year, the first payment on account deadline is 31 January 2027, and the second is 31 July 2027.

If 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’.

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

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

Failing to complete self-assessment on time means you could face paying a penalty of hundreds or even thousands of pounds depending on length of delay.

You’d also have to pay 7.75% interest on top (calculated as the Bank of England base rate plus 4%).

One day late

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

Three months late

After three months, 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.

Paying your tax bill late

You can also be hit with a penalty if you pay your tax late.

You get a penalty worth 5% of your tax bill if you have not paid your tax bill after 30 days.

This 5% penalty applies again at 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.

To ensure you aren’t stuck paying late penalties, it is a good idea to file your tax return earlier than the deadline.

Some people put off dealing with their paperwork because they can’t afford to pay their tax bill but this is a bad idea – anyone who may struggle to pay can contact HMRC about potentially setting up a payment plan.

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. Mistakes can be corrected within 12 months of the 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 to hit the tax return deadline on time and avoid overpaying

To avoid unnecessary stress involved with filing a self-assessment tax return correctly and on time, there are several steps you can take.

First and foremost, give yourself as much time as possible – the earlier you start, the better.

Gather together all the relevant paperwork before you start attempting to fill in the return – your payslips and P60, P45 or P11D forms, details of other income sources, savings and investments, pension contributions and charitable donations.

Understanding any applicable tax allowances and reliefs might help reduce the actual tax you have to pay.

Make sure you’re clear on any eligible expenses such as travel or uniform allowances. HMRC also allows up to £1,000 tax-free for casual income, like selling personal items or odd jobs.

Make sure everything is accurate before you submit – even errors made in good faith can incur penalty charges.

After you file for the relevant tax year, it’s worth planning ahead. Are there lessons you can apply to future years to reduce your tax bill?

Topping up your pension is a great way to lower your tax liability, as well as helping provide for your retirement.

Keep an eye on your tax code and check it remains accurate for your circumstances.