When Are Self Assessments Due?

Self Assessment is one of those areas of tax that many people know they need to deal with, but are not always entirely clear on the timing. The phrase “January deadline” is widely used, yet in practice there are several key dates throughout the year that matter just as much — sometimes more — depending on your circumstances.

Understanding when Self Assessments are due, and what each deadline actually relates to, can help reduce stress, avoid penalties, and make the process far more manageable.

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Who needs to file a Self Assessment?

Before looking at deadlines, it’s worth briefly revisiting who Self Assessment applies to. You may need to file a tax return if you have income that is not fully taxed at source, including:

• Self-employed or freelance income

• Rental or property income

• Dividend or investment income above allowances

• Capital gains from selling assets

• Multiple sources of income

• Child Benefit charges to declare

• Other untaxed or overseas income

Many people enter Self Assessment because their circumstances change, sometimes without realising straight away. This is why understanding the deadlines is important even if you are new to the process.

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The tax year: the starting point

The UK tax year runs from 6 April to 5 April. Each Self Assessment tax return covers income earned during that period.

For example:

• Income earned between 6 April 2024 and 5 April 2025 is reported on the 2024/25 tax return.

All deadlines are tied back to this tax year, rather than the calendar year.

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5 October: registering for Self Assessment

One of the most commonly missed deadlines comes much earlier than January.

If you need to file a Self Assessment tax return for the first time, you must register with HMRC by 5 October following the end of the tax year.

For example:

• If you had untaxed income in the 2024/25 tax year, you should register by 5 October 2025.

Missing this deadline does not remove the obligation to file, but it can complicate matters and increase the risk of penalties if things are delayed further.

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31 October: paper tax return deadline

If you are submitting a paper Self Assessment tax return, it must reach HMRC by 31 October following the end of the tax year.

Using the same example:

• For the 2024/25 tax year, the paper return deadline is 31 October 2025.

Most people now file online, but this deadline still applies to anyone submitting a paper return.

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31 January: the key Self Assessment deadline

The most well-known Self Assessment date is 31 January, and for good reason. This is the deadline for several important obligations.

By 31 January following the end of the tax year, you must:

• Submit your online Self Assessment tax return

• Pay any balancing tax due for that tax year

• Make your first payment on account, if applicable

For the 2024/25 tax year, all of the above are due by 31 January 2026.

This is why January is such a busy month for Self Assessment, and why planning ahead can make a significant difference.

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Payments on account: why January isn’t always the end

For many taxpayers, particularly the self-employed and landlords, January is not the final payment point.

If your tax bill is above a certain level and not mostly collected at source, HMRC may require payments on account. These are advance payments towards the following tax year’s bill.

Payments on account are due:

• 31 January (first payment)

• 31 July (second payment)

Each payment is typically 50% of the previous year’s tax bill, unless circumstances have changed.

This means that for some people, Self Assessment obligations continue well beyond January.

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31 July: the often-forgotten deadline

The 31 July payment on account deadline is frequently overlooked, as it falls outside the usual Self Assessment “season”.

By 31 July, you may need to:

• Pay your second payment on account for the current tax year

Although no tax return is due at this point, missing the payment can still result in interest and penalties. It is a deadline worth diarising early in the year.

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Why knowing the deadlines isn’t always enough

While knowing the dates is important, many of the challenges around Self Assessment arise not because people forget deadlines, but because everything is left until the last possible moment.

By January:

• The tax year has already ended

• Planning opportunities for that year have largely passed

• Cash flow decisions may already be fixed

This can make Self Assessment feel reactive and stressful, rather than controlled and predictable.

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Using the calendar to your advantage

Understanding when Self Assessments are due allows the process to be spread more evenly across the year.

For example:

• Early submission can provide clarity on upcoming tax bills

• Reviewing figures well before January allows time to plan for payments

• Identifying changes early can prevent unexpected liabilities

Many people find that once the pressure of deadlines is removed, Self Assessment becomes far more manageable.

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New to Self Assessment?

If you are newly self-employed, have started receiving rental income, or your circumstances have changed, deadlines can feel particularly unclear.

In these situations, questions often arise around:

• Whether you need to register
• What income needs to be reported
• When payments will be due
• How much to set aside

Getting clarity early can prevent issues later, particularly where payments on account or registration deadlines are involved.

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Self Assessment as part of the wider picture

Although Self Assessment is built around fixed dates, it does not need to be treated as a once-a-year event. In practice, it often works best when viewed as part of an ongoing review of income, tax, and future plans.

When approached this way, deadlines become reference points rather than sources of pressure.

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Understanding when Self Assessments are due is a crucial first step. Knowing how those dates fit into your wider financial position can make the process smoother, clearer, and far less stressful as the year progresses.