When do self-assessment tax returns need to be filed in the UK?

Understanding UK Self Assessment in plain English

Self Assessment is the UK system HM Revenue & Customs (HMRC) uses to collect Income Tax (and, in many cases, National Insurance) from people whose tax is not fully dealt with through PAYE. If you are an employee with a single job and nothing else going on, your tax is usually sorted automatically through your payslip. But once you start receiving income that is not taxed at source, or your tax affairs become more complicated, HMRC often requires you to submit a Self Assessment tax return so they can calculate what you owe and confirm you have paid the right amount.

The most common question people ask about Self Assessment is also the most important: when do the returns need to be filed? The short answer is that the filing deadline depends on whether you submit a paper return or file online, and both deadlines relate to the end of the relevant tax year. The long answer is more useful, because it includes registration deadlines, payment dates, late filing penalties, and practical tips for avoiding stress and surprise bills.

This article walks through the full UK Self Assessment timetable step by step, explains which tax year the deadlines refer to, and highlights what to do if you miss a date. By the end, you should have a clear picture of the exact deadlines that apply, how to plan ahead, and how to avoid the most common mistakes.

What tax year does a Self Assessment return cover?

In the UK, the tax year runs from 6 April to 5 April the following year. That means a Self Assessment return is always linked to a tax year that ends on 5 April.

For example, if you earned self-employed income between 6 April 2024 and 5 April 2025, that is the 2024/25 tax year. The return you submit will be a 2024/25 Self Assessment return, and the standard filing and payment deadlines will fall after 5 April 2025.

It is easy to get confused because the deadlines are in the following calendar year. Many people assume “the 2024 return” means the return filed in 2024. In practice, people often talk about the tax year in the format 2024/25, and the return is usually filed after the tax year has ended.

The main filing deadlines: paper vs online

There are two main ways to file a Self Assessment tax return: on paper or online. The deadlines are different, and online filing gives you longer.

Paper tax return deadline: 31 October

If you file a paper tax return, the deadline is 31 October following the end of the tax year. Using the earlier example, for the 2024/25 tax year ending on 5 April 2025, the paper return deadline would be 31 October 2025.

This deadline matters even if you plan to pay any tax due later. Filing on time helps you know what you owe and reduces the risk of penalties. Paper filing is less common now, but it is still used by some people who prefer it, need it for certain circumstances, or have limited online access.

One practical point: “filed” does not mean “posted.” If you are sending a paper return, it needs to reach HMRC by the deadline, not simply be in the post. Postal delays can and do happen, especially around busy periods. If you choose paper, build in plenty of time.

Online tax return deadline: 31 January

If you file your Self Assessment return online, the deadline is 31 January following the end of the tax year. Again using the 2024/25 example, the online filing deadline would be 31 January 2026.

Most people file online because it is quicker, the system does calculations automatically, and you can submit right up to the deadline (though leaving it to the last minute is rarely a good idea). Online filing also lines up with the most important payment deadline, which is also 31 January for many taxpayers.

It’s worth emphasising: 31 October is the paper filing deadline; 31 January is the online filing deadline. The date you must meet depends on the method you use.

Registration deadlines: when you need to tell HMRC you’re doing Self Assessment

Before you can file a Self Assessment return, you generally need to be registered with HMRC for Self Assessment. Registration is a separate step from filing, and it has its own deadlines. People often discover Self Assessment deadlines only after they have already missed the registration cut-off, which can create a messy scramble.

Newly self-employed: tell HMRC by 5 October

If you start working for yourself (as a sole trader) or begin receiving income that means you need to complete a tax return, you typically need to notify HMRC by 5 October following the end of the tax year in which you started.

For example, if you started self-employment in the 2024/25 tax year (any time between 6 April 2024 and 5 April 2025), you would normally need to register for Self Assessment by 5 October 2025.

Missing the 5 October notification date does not necessarily mean you cannot file; it usually means you are late telling HMRC and may need to act quickly to get set up. Registration can take time because you may need to receive activation codes by post.

Why registration matters for deadlines

Even if you fully intend to file online by 31 January, you cannot do that smoothly unless you have the right credentials and are enrolled. If you wait until January to register, you may run out of time to receive login details or activation codes. Many late filers are not late because they forgot the deadline; they are late because they left registration too late.

If you already filed in previous years, you are typically already registered. The key group that needs to think about registration is people filing for the first time: new sole traders, new landlords, people with new side income, or people who have become directors with more complex remuneration.

Payment deadlines: filing is only half the story

A Self Assessment return is about reporting. The next part is paying. Many people assume that once they file, they are done. In reality, filing and paying have separate deadlines, and you can file on time but still be charged interest or penalties if you pay late.

Balancing payment deadline: 31 January

For most people, the main payment deadline is 31 January following the end of the tax year. This is the date by which any remaining tax due for that tax year must be paid. It is sometimes called the “balancing payment” because it balances the tax bill after any tax already paid (for example, via PAYE or tax deducted at source).

Using the 2024/25 example: the balancing payment is due by 31 January 2026.

This is also the online filing deadline, which is why January becomes such a pressure point. People file their return in January, see a tax bill, and then have to pay it almost immediately. The earlier you file, the earlier you know what you owe and the more time you have to plan.

Payments on account: 31 January and 31 July

If your Self Assessment tax bill is above a certain level and you meet the criteria, HMRC may require “payments on account.” These are advance payments towards your next year’s tax bill, paid in two instalments. The idea is to stop taxpayers from paying large sums long after the income was earned.

Payments on account are normally due on:

1) 31 January (the first payment on account for the next tax year, due at the same time as the balancing payment for the previous year)

2) 31 July (the second payment on account for the next tax year)

So, in a typical cycle, 31 January is a double deadline: you may owe a balancing payment for the year you are reporting, plus the first payment on account for the next year. Then 31 July comes around with the second payment on account.

This is one reason Self Assessment can feel expensive: you might see what looks like “two years of tax.” It is often not two full years; it is the current year’s bill plus an advance payment towards the next year. If your income drops significantly, it may be possible to reduce payments on account, but that needs careful handling because underpaying can lead to interest.

Timeline example: the full cycle for a typical tax year

Sometimes the easiest way to understand deadlines is to see them laid out as a timeline. Here is how it usually works for a tax year that ends on 5 April.

6 April to 5 April: You earn income in the tax year and keep records.

After 5 April: The tax year ends, and you can begin preparing your Self Assessment return.

By 5 October: If it is your first time needing a return for that tax year, you generally need to notify HMRC / register for Self Assessment by 5 October.

By 31 October: If you are filing on paper, your return must reach HMRC by 31 October.

By 31 January: If you are filing online, your return must be submitted by 31 January. This is also the deadline to pay any tax due for that tax year (balancing payment) and, if applicable, the first payment on account for the next tax year.

By 31 July: If payments on account apply, the second instalment is due by 31 July.

Once you see it this way, the pattern becomes predictable. The biggest takeaway is that you can work on your return as soon as the tax year ends, and filing early can reduce stress and improve cash planning.

What happens if you miss the filing deadline?

Missing the deadline is not the end of the world, but it can get expensive quickly. HMRC’s late filing penalties are structured to encourage prompt submission. The longer you leave it, the more it can cost, even if you do not owe much tax.

Immediate fixed penalty after the deadline

If you file your Self Assessment return after the deadline, you normally face an automatic fixed penalty. This applies even if you have no tax to pay or have already paid all tax due. In other words, the penalty is about late filing, not just late payment.

Because the fixed penalty can arise right away after the deadline, it’s usually better to file something on time, even if you are not perfectly organised, and then correct it if needed (within the relevant amendment rules) rather than delaying and triggering penalties.

Additional penalties as time passes

If the return remains outstanding for longer, further penalties can apply at set points. These can include daily penalties after a certain period, followed by additional penalties at later milestones, and potentially a percentage-based penalty if the return is very late.

The exact structure can be complex, and it may depend on whether the delay is three months, six months, or twelve months, as well as whether there is tax unpaid. The important practical message is simple: late filing can snowball, so the best time to act is as soon as you realise you are late.

What if you miss the payment deadline?

Late payment has its own consequences, separate from late filing. Even if you file on time, paying after the deadline can lead to interest charges and late payment penalties. If you pay late and also file late, you can be hit from both sides.

Interest on late payments

HMRC typically charges interest on overdue tax from the day after the payment deadline until the day the tax is paid. Interest can apply even if the late payment penalties have not yet been triggered. Because interest is calculated over time, the longer you wait, the more it costs.

Late payment penalties

In addition to interest, late payment penalties can apply when tax remains unpaid after certain periods. These penalties are usually based on a percentage of the tax outstanding. Again, the headline point is that waiting makes it worse, and paying as soon as possible limits damage.

If you can’t pay: what to do instead of ignoring it

People sometimes avoid filing because they are worried about paying. That often backfires. Filing is about declaring your position; paying is about settling it. If you know you may struggle to pay by the deadline, it is still usually better to file on time, see the bill, and then explore options.

In many cases, HMRC may offer a payment plan (often referred to as a “Time to Pay” arrangement) depending on your circumstances and compliance history. The earlier you engage, the more options you tend to have. Ignoring the problem can lead to escalating penalties and enforcement action.

Who needs to file a Self Assessment tax return?

Deadlines only matter if you have to file, so it helps to understand the common reasons someone ends up in Self Assessment. Not everyone with extra income needs to submit a return, and some people are brought into Self Assessment for a period and later taken out. The requirement depends on your specific situation and HMRC’s criteria at the time.

Common groups who may need to file include:

Sole traders and self-employed people who run their own business, including freelancers and contractors.

Landlords who receive rental income from property (in the UK or sometimes overseas, depending on residence and rules).

Company directors in certain circumstances, particularly if their affairs are not fully handled through PAYE.

People with significant untaxed income such as large amounts of savings interest, dividends, foreign income, or income from side gigs where tax is not already deducted.

High-income individuals who need to pay specific charges, repay child benefit (the High Income Child Benefit Charge), or have complexities that mean HMRC requires a return.

People with capital gains who have sold assets and owe Capital Gains Tax beyond allowances or reporting thresholds.

If you are unsure whether you need to file, it is important to check early, because “finding out in January” is exactly how people fall into late registration or late filing.

Online filing: why it’s usually the simplest choice

Because the online deadline is later, most people choose to file electronically. Online filing also offers practical advantages: the system prompts you through sections, does calculations, and gives you immediate confirmation of submission.

Online filing can reduce simple arithmetic errors and helps you understand your tax position earlier. You can also save progress and return to the form, which is helpful if you are still waiting for information like bank interest certificates, dividend vouchers, or finalised accounts.

That said, online filing does not remove the need for good record keeping. If you enter incorrect figures, the system will still produce a confident-looking result. The responsibility for accuracy remains yours.

Paper filing: when it might still be relevant

Paper filing is less popular, but there are situations where people still consider it. Some taxpayers prefer paper for personal reasons, and a small number may have circumstances where paper processes are used. However, because the paper deadline is earlier, choosing paper usually means committing to earlier preparation.

If you are thinking about paper filing, the best approach is to treat the 31 October deadline as non-negotiable and start preparing soon after the tax year ends. You should also factor in postal time and the possibility of delays.

Amending a return: what if you file and later find a mistake?

Even careful people make mistakes: a missing expense, a forgotten bank account, or a corrected figure from a client. The good news is that the system allows amendments in many cases. The key point for deadlines is that amending is different from filing.

You still need to file by the relevant filing deadline. If you later discover an error, you can usually correct it by submitting an amendment within the amendment window. If you miss the filing deadline while waiting to “get it perfect,” you could incur a penalty that might have been avoided.

From a practical standpoint, it is often better to file on time with the best information you have, then amend if necessary. If the amendment results in more tax due, paying promptly limits interest and penalties. If the amendment results in less tax, you may be due a refund or a reduced bill.

Common deadline mistakes and how to avoid them

Most Self Assessment problems are predictable. They happen because people misread which year the deadline applies to, underestimate how long preparation takes, or forget that filing and paying are separate. Here are the most common mistakes and how to sidestep them.

Mistake 1: Confusing the tax year with the calendar year

Remember that the tax year ends on 5 April, not 31 December. If you keep thinking in calendar years, you may end up preparing the wrong period or assuming you have more time than you do. A simple fix is to label folders and documents by tax year (for example, “2024/25”) so you always know what you are working on.

Mistake 2: Leaving registration until January

If you have never filed before, registration can involve waiting for activation codes. Waiting until the month of the deadline is risky. If you think you might need to file, investigate early and complete registration well before winter.

Mistake 3: Filing on time but forgetting the payment

Submitting the return is not the same as paying the bill. Build a habit of checking the calculation after filing and setting aside the funds (or arranging payment) promptly. If payments on account apply, plan for both January and July.

Mistake 4: Not keeping records during the year

People who keep tidy records find Self Assessment dramatically easier. If you leave record keeping until the last minute, you are more likely to miss expenses, forget income, or rush. A simple monthly routine of updating income and expenses can reduce your filing time from days to hours.

Mistake 5: Ignoring HMRC letters and messages

Sometimes people miss deadlines because they miss communications. If you move house, make sure HMRC has your current address. If you use online services, check your account regularly during busy periods so you don’t miss reminders or notices.

Practical tips for meeting the deadlines comfortably

Meeting Self Assessment deadlines is mostly about planning. You do not need an elaborate system; you need a dependable one. Here are practical approaches that help many taxpayers stay calm and on track.

File early, even if you pay later

You can usually file your return well before the payment deadline. Filing early tells you what you owe and reduces the January shock. You do not have to wait until you are ready to pay to submit the return. In many cases, the biggest benefit of early filing is psychological: you replace uncertainty with a clear number.

Set aside money as you earn it

If you are self-employed or have untaxed income, tax can feel painful because it arrives as a big bill. A practical way to reduce stress is to set aside a percentage of income into a separate account as you go. The right percentage depends on your overall circumstances, but the principle is what matters: treat tax as a cost that accrues over time, not a surprise at the end.

Keep a “tax pack” folder

Create a folder (digital or physical) where you put anything that might be relevant: invoices, receipts, statements, mileage logs, pension contributions, charitable donations, and so on. If you do this throughout the year, preparing the return becomes a process of summarising rather than hunting.

Use reminders for key dates

Key dates worth putting in your calendar include 5 October (notification/registration for first-time filers), 31 October (paper), 31 January (online and main payment), and 31 July (second payment on account if relevant). Even if you always file online, having the paper deadline in mind can act as an earlier “soft deadline” to push you into action.

Consider professional help if your affairs are complex

Some tax returns are straightforward. Others involve multiple income streams, foreign income, capital gains, property, or business complications. If your situation is complex or time-consuming, getting advice can help you file accurately and potentially avoid expensive mistakes. The key is to arrange help early rather than in the final week of January when everyone is busy.

Special situations that can affect deadlines

The standard deadlines apply to most taxpayers, but real life is messy. A few situations are worth flagging because they can change what you need to do or how urgently you need to act.

First-time returns and Unique Taxpayer Reference (UTR)

If you are filing for the first time, you will typically need a Unique Taxpayer Reference. Getting set up can take time. This doesn’t change the statutory filing deadline, but it changes your personal timeline because you need to allow for administration and login setup.

Stopping Self Assessment

If you no longer need to file Self Assessment because your affairs have simplified, you may be able to stop filing in future years. But do not assume you can simply skip a year. If HMRC issues a notice to file, you generally need to submit a return or formally resolve the requirement. The safe approach is to confirm your obligations rather than guessing.

Moving abroad or having foreign income

International situations can add complexity and may require extra pages or additional information. The deadlines are usually the same, but preparation may take longer because you might need overseas statements, exchange rate conversions, or advice on residence status.

Why the deadline matters beyond penalties

It is tempting to view deadlines as purely about avoiding fines. In reality, filing on time has broader benefits. It keeps your financial records up to date, helps with mortgage applications and proofs of income, supports benefit or loan assessments that rely on taxable income, and reduces the risk of HMRC enquiries triggered by missing information or late submissions.

For business owners, timely tax compliance also supports better decision-making. When you know your profit and tax position early, you can plan investments, pension contributions, and cash flow with confidence rather than guesswork.

A quick checklist of the key UK Self Assessment dates

If you only remember one part of this article, remember this set of dates and what they mean:

5 April: Tax year ends.

5 October: Common deadline to notify HMRC / register for Self Assessment for that tax year if you have not filed before and now need to.

31 October: Deadline for paper tax returns.

31 January: Deadline for online tax returns and the main deadline for paying tax due for the year (balancing payment), plus the first payment on account for the next year if applicable.

31 July: Deadline for the second payment on account if applicable.

Final thoughts: the simplest way to stay on time

UK Self Assessment deadlines are consistent and predictable once you anchor them to the end of the tax year. The return relates to the tax year that ends on 5 April. If you file on paper, the deadline is 31 October after that. If you file online, the deadline is 31 January after that. Payment is normally due by 31 January, with a possible additional payment on 31 July if payments on account apply.

The easiest way to avoid last-minute panic is to treat Self Assessment as a year-round process rather than a January task. Keep basic records as you go, register early if it is your first time, file earlier than you think you need to, and plan for the payment dates. If you do that, the deadlines stop feeling like traps and start feeling like simple checkpoints.

And if you do miss a deadline, the key is to act quickly: file as soon as you can, pay what you can, and communicate early if payment is difficult. In most cases, prompt action reduces costs and prevents small problems from turning into large ones.