What is the Self Assessment tax deadline UK

Self Assessment tax deadline UK: the quick answer

When people ask “What is the Self Assessment tax deadline in the UK?”, they are usually talking about the big January cut-off: the deadline to file your online Self Assessment tax return and to pay any tax you owe for the previous tax year is 31 January (by 11:59pm for filing online, and by that date for payment). For many taxpayers, this date is the single most important one to remember because it can trigger penalties if you miss it.

However, Self Assessment has more than one deadline. There are different dates for paper returns, for registering, for “payments on account” (which can create a second payment deadline in July), and for people who need to start completing a tax return for the first time. This article breaks down every key Self Assessment deadline in plain English, explains how the dates fit together across the tax year, and highlights the most common reasons people get caught out.

What Self Assessment is (and who the deadlines apply to)

Self Assessment is the system HMRC uses to collect Income Tax (and, in some cases, National Insurance and other taxes) from people whose tax is not fully settled through PAYE. You might need to use Self Assessment if you are self-employed as a sole trader, you receive income from property, you have significant untaxed income, you need to claim certain reliefs, or HMRC has asked you to file a return. Some company directors and people with more complex tax affairs also use Self Assessment, although not every director needs to file.

The key point is that the deadlines apply once you are required to file. If HMRC issues you a notice to file a tax return (or you meet the criteria that require a return), you’re expected to submit by the relevant deadline even if you think you owe no tax. Missing the filing deadline can lead to penalties, and missing the payment deadline can lead to interest and late payment penalties.

Understanding the tax year: why the deadline feels “late”

The UK tax year runs from 6 April to 5 April. That can be confusing because the most talked-about deadline is 31 January, which falls after the tax year ends. For example, the tax year ending on 5 April is followed by the filing and payment deadlines later in the same calendar year (for paper) and the next January (for online and payment).

The reason the system is set up this way is practical: you need time after 5 April to gather information, calculate your totals, claim allowable expenses and reliefs, and then submit the return. But the spacing between the end of the tax year and the deadline can create a false sense of security. If you wait until January to start, you can easily run out of time—especially if you need help from an accountant, are waiting on missing statements, or have to untangle multiple income sources.

The main Self Assessment deadlines you need to know

There are four headline deadlines that cover most people’s obligations. Depending on your situation, you may need to meet all of them, or only some.

1) Registering for Self Assessment (first-time filers)

If you’ve never filed a tax return before, you may need to register so HMRC can set you up with a Unique Taxpayer Reference (UTR) and (if you’re filing online) give you access to the online service. Registration has its own deadline, which is separate from the filing deadline.

The registration deadline often catches new self-employed people who start trading part-way through the tax year. If you begin self-employment, you may assume that nothing is due until the January filing deadline—but you can’t file online until you’re properly set up, and HMRC processes can take time. In other words: if you are new to Self Assessment, treat registration as a “pre-deadline” and do it early.

Practical tip: even if you’re not sure what your final profit will be, it’s still wise to register as soon as you know you’ll need to file. Sorting out the admin early reduces the risk of a last-minute panic.

2) The paper tax return deadline: 31 October

If you file a paper Self Assessment tax return, the deadline is earlier than the online deadline. The paper deadline is typically 31 October after the end of the tax year. Paper filing is less common now, but some people still use it, and it can be relevant if you cannot file online.

Because paper returns must be received and processed, leaving it late is risky. Postal delays, missing pages, and errors can all cause problems. If you are filing on paper, build in extra time and consider using tracked post so you have proof of sending and delivery.

3) The online tax return deadline: 31 January

If you file your Self Assessment return online, the deadline is typically 31 January following the end of the tax year. This is the date most people mean when they talk about “the Self Assessment deadline.” It’s also the deadline that generates the last-minute rush every year.

Filing online is usually quicker, provides immediate confirmation, and reduces the risk of lost paperwork. But “online” doesn’t mean “instant.” If you don’t already have access to the online service, you may need to wait for activation codes or complete identity checks. That’s why early registration matters.

4) The payment deadline: 31 January (and sometimes 31 July)

In addition to filing your return, you normally have to pay your Self Assessment tax bill by 31 January. This payment is often referred to as a “balancing payment” because it’s the amount needed to settle your tax liability for the year after taking into account any tax already paid.

Many people also have to make payments on account. These are advance payments towards the next tax year’s bill, usually split into two instalments:

• 31 January: first payment on account for the current year (plus any balancing payment for the previous year).
• 31 July: second payment on account for the current year.

This creates a common surprise: you file your return, see a tax bill, and expect to pay only what you owe for that year—but your January bill might include both the balancing payment and the first payment on account for the following year. That can make the January payment feel unusually large.

Why 31 January is such a big deal

31 January matters because it is the point where multiple obligations can collide: it can be the deadline to file your online return, the deadline to pay your balancing payment, and the deadline to make your first payment on account. If you miss it, you may face late filing penalties and late payment consequences at the same time.

It’s also psychologically difficult because it arrives right after December holidays and at a time of year when people’s personal finances can be stretched. That’s why planning ahead—especially if you rely on Self Assessment income—is so important.

What happens if the deadline falls on a weekend or bank holiday?

In many areas of UK administration, deadlines that land on non-working days shift to the next working day. With Self Assessment, the safest approach is to assume the deadline is the deadline and aim to complete everything before the date. For online filing, you can generally submit right up to 11:59pm on the deadline day. For payments, processing times and bank cut-off times can matter—so leaving payment until the final evening is risky.

If you pay by bank transfer, debit card, or other methods, the time it takes for funds to reach HMRC can vary. The practical best practice is simple: file early, pay early, and never rely on “next working day” assumptions.

Late filing penalties: what you risk if you miss the filing deadline

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