Self Assessment Deadlines 2027: Key Dates You Shouldn’t Miss

If you need to complete a Self Assessment tax return, keeping track of HMRC deadlines is essential. Missing an important date could result in penalties, interest charges and unnecessary stress.

For taxpayers completing a return for the 2025/26 tax year (6 April 2025 to 5 April 2026), the main online filing and payment deadline is 31 January 2027. However, there are several other important dates you should know about.

This guide explains the key Self Assessment deadlines for 2026 and 2027, from registering with HMRC to submitting your return and paying your tax bill.

Key Self Assessment Dates for 2026/27

Here are the main dates to add to your calendar:

HMRC confirms that the 2025/26 online tax return and tax due must normally be dealt with by 31 January 2027.

5 October 2026 – Register for Self Assessment

If you need to file a Self Assessment return for the first time for the 2025/26 tax year, you should tell HMRC and register by 5 October 2026.

This may apply if, for example, you have become self-employed or have income that needs to be reported through Self Assessment.

HMRC has confirmed that taxpayers who need to file for the first time for 2025/26 should register by 5 October 2026.

Registering early gives you more time to receive your Unique Taxpayer Reference (UTR) and prepare your tax return before January.

31 October 2026 – Paper Tax Return Deadline

If you are submitting your Self Assessment return on paper, HMRC must normally receive it by 31 October 2026.

The paper filing deadline arrives three months before the standard online deadline, so it is important to decide how you intend to submit your return well in advance.

Most taxpayers now choose to file electronically because it provides additional time and makes calculating the tax liability more straightforward.

31 January 2027 – Online Self Assessment Deadline

The most important date for many taxpayers is 31 January 2027.

Your online Self Assessment tax return for the 2025/26 tax year must normally be submitted to HMRC by this date.

Waiting until January can create unnecessary pressure, particularly if you discover that information is missing or need clarification regarding expenses, income or other tax matters.

Submitting your return earlier gives you more time to understand your tax position and prepare for the payment deadline. HMRC also highlights budgeting as one of the benefits of filing early.

31 January 2027 – Paying Your Self Assessment Tax Bill

Filing your return is only part of the process.

Any balancing payment for the 2025/26 tax year will generally also need to be paid by 31 January 2027.

Depending on your circumstances, your January payment could include:

This is why your January payment can sometimes be significantly higher than expected.

What Are Payments on Account?

Payments on Account are advance payments towards your next Self Assessment tax bill.

If they apply to you, HMRC normally requires two instalments:

First Payment on Account: 31 January
Second Payment on Account: 31 July

Each Payment on Account is normally 50% of the relevant previous year’s tax liability.

For example, if the relevant amount used to calculate your Payments on Account is £4,000, you could normally be asked to pay:

Your actual tax liability is then finalised when the next Self Assessment return is completed.

Payments on Account generally do not apply if your previous year’s relevant tax bill was less than £1,000, or if more than 80% of the tax you owed was collected outside Self Assessment.

31 July 2027 – Second Payment on Account

If Payments on Account apply to you for the 2026/27 tax year, your second Payment on Account will normally be due by 31 July 2027.

It is important not to overlook this deadline simply because your annual tax return is not due in July.

If you expect your income or tax liability to be lower, it may be possible to apply to reduce your Payments on Account. However, they should not be reduced without a reasonable basis because interest may be charged if you reduce them too far.

What Happens If You Miss the Self Assessment Deadline?

Missing a Self Assessment filing or payment deadline can lead to penalties and interest.

HMRC states that taxpayers may have to pay interest and a penalty if they fail to file and pay on time.

Even if you cannot immediately afford your tax bill, ignoring the deadline is rarely the right approach. You should establish what you owe and consider the available payment options as early as possible.

Why File Your Tax Return Early?

There is no need to wait until January to submit your Self Assessment return.

Once the tax year has ended and you have the necessary information, filing early can provide several benefits:

Importantly, filing your return early does not normally mean you have to pay your tax early. HMRC confirms that taxpayers who submit early can still wait until the relevant payment deadline to settle their bill.

What Records Should You Prepare?

The exact documents required depend on your circumstances, but you may need records relating to:

HMRC requires taxpayers to keep appropriate records, such as receipts and bank statements, so their Self Assessment return can be completed accurately.

Don’t Leave Your 2025/26 Tax Return Until January

The 31 January 2027 Self Assessment deadline may seem a long way away, but preparing early can make the entire process easier.

Getting your records together ahead of time gives you an opportunity to identify missing information, understand your tax liability and plan for any payment due.

At Legacy Accounting, we can assist with preparing and submitting your Self Assessment tax return, reviewing your income and allowable expenses, calculating your tax liability and helping you understand what needs to be paid and when.

If you need support with your 2025/26 Self Assessment tax return, contact Legacy Accounting and get your return organised well ahead of the January deadline.

Frequently Asked Questions About Self Assessment Deadlines 2027

What is the Self Assessment deadline for 2027?

For most taxpayers filing online, the deadline for submitting the 2025/26 Self Assessment tax return is 31 January 2027. Any balancing tax payment due for the year will normally also need to be paid by this date.

When can I submit my 2025/26 Self Assessment tax return?

The 2025/26 tax year ended on 5 April 2026, so you can prepare and submit your return after the tax year has ended. There is no requirement to wait until January.

What is the paper tax return deadline for 2025/26?

The standard deadline for submitting a paper Self Assessment return for 2025/26 is 31 October 2026.

When do I need to register for Self Assessment?

If you need to complete Self Assessment for the first time for the 2025/26 tax year, the relevant registration deadline is 5 October 2026.

When does my Self Assessment tax need to be paid?

The balancing payment for the 2025/26 tax year is normally due by 31 January 2027. If Payments on Account apply, you may also have a first Payment on Account due on the same date.

What is the Payment on Account deadline in July 2027?

The second Payment on Account towards the 2026/27 tax year is normally due by 31 July 2027.

Do I have to pay my tax immediately if I submit my return early?

No. Filing your return early does not normally bring forward the standard payment deadline. For the 2025/26 tax year, tax due through Self Assessment is generally payable by 31 January 2027.

Can I reduce my Payments on Account?

You may be able to reduce your Payments on Account if you reasonably expect your tax liability to be lower. Care is needed because HMRC can charge interest if the payments are reduced below the amount that should ultimately have been paid.

Can an accountant submit my Self Assessment tax return for me?

Yes. An accountant can prepare your tax return, review the information provided, calculate your tax liability and submit the return to HMRC as your authorised agent.

Should I wait until January to contact an accountant?

It is usually better to start earlier. Preparing your Self Assessment return ahead of the deadline provides more time to obtain missing records, deal with queries and plan for the tax payment due on 31 January.

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