If you need to file a Self Assessment tax return for the 2025/26 tax year, the main UK tax deadline is 31 January 2027. You may also have earlier deadlines for registering, filing a paper return or choosing to have eligible tax collected through PAYE. Missing a deadline can result in penalties and interest, so knowing which date applies to you is important.
UK Tax Deadline: Key Self Assessment Dates
All the dates below apply to the 2025/26 tax year, which finished on 5 April 2026.
| UK tax deadline | What you need to do |
|---|---|
| 5 October 2026 | Sign up for Self Assessment if this will be your first return |
| 31 October 2026 | Submit a paper tax return |
| 30 December 2026 | Submit your online return if you want eligible tax collected through PAYE |
| 31 January 2027 | File your online return and pay any tax you owe |
| 31 January 2027 | Pay your first Payment on Account where it applies |
| 31 July 2027 | Pay your second Payment on Account where it applies |
HMRC‘s official Self Assessment deadlines page confirms that online returns and payments for the 2025/26 tax year are due by 31 January 2027.
What Happens If You Miss the Self Assessment Deadline?
Missing the deadline for your Self Assessment tax return can lead to a late filing penalty. If you also pay your tax late, separate late-payment penalties and interest can apply.
The important point is that filing your tax return and paying your tax bill are separate responsibilities. If you cannot pay the full amount, you should still submit your return on time and deal with the payment separately.
5 October 2026 — Deadline to Register for Self Assessment
First-time filers for 2025/26 normally need to register with HMRC by 5 October 2026.
This can apply if you became self-employed, started receiving certain untaxed income or otherwise became responsible for reporting income through Self Assessment.
HMRC says the same in its guidance: anyone filing for the first time for 2025/26 must register by 5 October 2026.
Registering after 5 October may mean HMRC sets you a different deadline for submitting your return. The tax you owe, however, is still generally due by 31 January 2027.
That date has now passed. If you became self-employed in the 2026/27 tax year (6 April 2026 to 5 April 2027), you must register by 5 October 2027.
31 October 2026 — Paper Tax Return Deadline
A paper Self Assessment tax return has to reach HMRC by 31 October 2026.
This is three months earlier than the online filing deadline, so taxpayers who file online have additional time to prepare and submit their return.
30 December 2026 — Paying Through Your Tax Code
Some taxpayers may be able to have their Self Assessment bill collected through their PAYE tax code.
To use this option, eligible taxpayers need to file their online tax return by 30 December 2026.
Miss that date and you will normally have to settle your Self Assessment bill another way.
31 January 2027 — Main Online Filing and Payment Deadline
For the majority of online filers, the main UK tax deadline for the 2025/26 Self Assessment return is 31 January 2027.
By this date, you generally need to:
- Submit your 2025/26 online tax return
- Pay your balancing payment for 2025/26
- Make your first Payment on Account towards the next tax year, where it applies
There is no need to wait until January to file. You can submit your return from 6 April 2026, which gives you more time to understand what you owe and plan for the payment.
31 July 2027 — Second Payment on Account
Where Payments on Account apply, the second instalment is normally due by 31 July 2027.
Payments on Account are advance instalments towards your following tax bill, usually paid on 31 January and 31 July.
Self Assessment Late Filing Penalties
Send your return in after the deadline and HMRC can charge a series of late filing penalties.
One Day Late — £100 Penalty
An initial £100 penalty can apply if your Self Assessment tax return is late, even if you have no tax to pay.
Three Months Late or More — Daily Penalties
If the return is still outstanding after three months, HMRC can charge £10 per day, for a maximum of 90 days.
That means daily penalties can reach £900.
More Than 6 Months Late
Once the return is six months overdue, a further penalty can be added: the greater of 5% of the tax due or £300.
More Than 12 Months Late
At 12 months, a second charge of the same size can be added: 5% of the tax due or £300, whichever is higher.
| How late is your return? | Potential penalty |
|---|---|
| 1 day late | £100 |
| More than 3 months late | £10 per day, up to £900 |
| More than 6 months late | The greater of 5% of tax due or £300 |
| More than 12 months late | The greater of 5% of tax due or £300 |
These are the current Self Assessment late-filing penalties. Making Tax Digital for Income Tax is HMRC’s newer way of reporting income, and different rules can apply to taxpayers who come within it, but the current penalties still cover the 2025/26 return due on 31 January 2027.
Self Assessment Late Payment Penalties
Filing late and paying late are two separate matters.
If your return is filed on time but the tax is not paid by the payment deadline, HMRC can still charge late-payment penalties.
Under the current Self Assessment rules, penalties of 5% of the unpaid tax can apply at:
- 30 days late
- 6 months late
- 12 months late
HMRC can also charge interest on the unpaid amount.
This is why submitting your return on time is only part of the process. The payment itself needs planning too.
How Much Interest Does HMRC Charge on Late Tax?
HMRC charges interest when certain tax payments are made late.
For Income Tax and Self Assessment, the late-payment interest rate is currently 7.75% from 9 January 2026. HMRC can change its interest rates, so taxpayers should check the latest official rate before making a payment.
Interest is separate from late-payment penalties. If you pay your tax late, you may therefore have both interest and penalties to deal with.
Realised you have underpaid? Read what to do if you have underpaid HMRC.
What Are Payments on Account?
Payments on Account are advance payments towards your next Self Assessment tax bill.
They are normally made in two instalments:
- 31 January
- 31 July
Each payment is usually half of the previous year’s relevant tax bill.
You normally do not have to make Payments on Account if your previous year’s tax was less than £1,000, or if more than 80% of your tax was already collected outside Self Assessment, subject to HMRC‘s rules.
Example of Payments on Account
Suppose your Self Assessment tax bill is £4,000.
If Payments on Account apply, you could have:
- £4,000 balancing payment
- £2,000 first Payment on Account
- £2,000 second Payment on Account
This means your January payment could be £6,000, followed by another £2,000 in July.
Understanding this before the deadline can help you avoid an unexpected cash-flow problem.
What If You Cannot Pay Your Self Assessment Tax Bill?
If you cannot afford to pay your full tax bill by the deadline, do not ignore the return.
You should:
- File your Self Assessment return on time.
- Pay as much as you can.
- Check whether you are eligible for an HMRC payment arrangement.
- Contact HMRC if you need help managing the outstanding amount.
HMRC also provides a Budget Payment Plan, which can allow eligible taxpayers to make regular payments towards a future Self Assessment bill.
The important thing is to deal with the problem early rather than allowing penalties and interest to build up unnecessarily.
Can You Appeal a Self Assessment Penalty?
Yes, you may be able to appeal a Self Assessment penalty if you had a reasonable excuse for missing the deadline.
HMRC considers the circumstances of each case. Having a reason does not automatically mean that a penalty will be cancelled.
If you believe you had a reasonable excuse, you should follow HMRC‘s appeal process and provide the relevant details and evidence.
Who Needs to File a Self Assessment Tax Return?
Not everyone needs to complete a Self Assessment tax return.
You may need to file if you:
- Are self-employed as a sole trader
- Are a partner in a business partnership
- Receive certain rental income
- Receive certain untaxed income
- Have foreign income that needs to be reported
- Receive certain investment or dividend income
- Have another reason that requires you to report income to HMRC
If you are unsure whether you need to file, HMRC provides an online checker to help you determine whether you need a tax return.
For sole traders, this is particularly important because registration and filing requirements can apply even if you have only recently started trading. For a step-by-step walkthrough, read our Self Assessment tax return guide for sole traders.
If you are a sole trader and need help managing your accounts and Self Assessment obligations, you can learn more about Sole Trader Accounts from Fair Accountants.
How to Avoid Self Assessment Penalties
The easiest way to avoid unnecessary penalties is to prepare before your UK tax deadline.
1. Know Your Deadline
Check whether you need to register, file a paper return or submit your return online.
2. Keep Your Records Organised
Keep records of your income, invoices, bank transactions and allowable business expenses throughout the year. Fair Accountants‘ bookkeeping services can take this off your plate.
3. Set Money Aside for Tax
If you are self-employed or receive untaxed income, don’t assume that all the money in your bank account is available to spend.
Set aside money towards your expected tax bill.
4. File Early
You do not have to wait until January.
Filing early can help you understand what you owe, identify mistakes and give you more time to plan for the payment. HMRC actively encourages taxpayers to file early.
5. Plan for Payments on Account
If Payments on Account apply to you, remember that your January bill can include both your balancing payment and your first payment towards the following year.
6. Get Professional Help When Needed
If you are unsure about your tax return, allowable expenses, deadlines or payments, getting professional accounting advice can help you avoid mistakes and stay compliant.
Self Assessment Checklist
Before submitting your return, make sure you have:
- Income records
- Sales and invoice records
- Relevant bank statements
- Allowable expense records
- Details of other taxable income
- Pension information where relevant
- Details of tax already paid
- Information needed for relevant tax reliefs
- Your HMRC login details
- Money set aside for your tax bill
You generally do not send receipts with your tax return, but you must keep appropriate records in case HMRC needs to check your return.
Frequently Asked Questions
What is the UK tax deadline for Self Assessment?
For the 2025/26 tax year, the main UK tax deadline for an online Self Assessment return and payment of tax owed is 31 January 2027. Other deadlines apply to registration, paper returns and PAYE tax-code collection.
What is the deadline for a Self Assessment tax return?
For the 2025/26 tax year, the online Self Assessment tax return deadline is 31 January 2027. Paper returns generally need to reach HMRC by 31 October 2026.
What happens if I file my tax return one day late?
You can receive an initial £100 late-filing penalty, even if you have no tax to pay. Further penalties can apply if the return remains outstanding.
What is the £100 Self Assessment penalty?
The £100 penalty is the initial late-filing penalty that can apply when a Self Assessment tax return is submitted after its deadline.
When is the Self Assessment payment deadline?
For the 2025/26 tax year, the main tax payment deadline is 31 January 2027. If you have Payments on Account, the second payment is normally due on 31 July 2027.
When is the second Payment on Account due?
The second Payment on Account is normally due on 31 July. For the 2025/26 tax year, this means 31 July 2027.
Can I appeal a Self Assessment penalty?
Yes. If you have a reasonable excuse for missing the deadline, you may be able to appeal the penalty. HMRC considers the circumstances of each case.
What counts as a reasonable excuse for a late tax return?
A reasonable excuse depends on the circumstances of the individual case. If you believe you had a reasonable excuse, you can appeal the penalty and explain what happened.
What happens if I cannot pay my Self Assessment tax?
You should still submit your return on time. If you cannot pay the full amount, check whether you can arrange payments with HMRC rather than ignoring the bill.
Can I arrange a payment plan with HMRC?
In some circumstances, HMRC may allow you to spread your tax payments. You should contact HMRC as soon as possible if you are struggling to pay.
Don’t Leave Your Tax Return Until the Last Minute
The UK tax deadline is not just a date to put in your calendar. Missing your filing or payment deadline can lead to penalties and interest.
If you are preparing your 2025/26 Self Assessment tax return, start gathering your records now rather than waiting until January.
Fair Accountants can help sole traders and self-employed individuals prepare their Self Assessment tax returns, understand their tax obligations and plan for upcoming payments.
Need help before the deadline? Contact Fair Accountants to discuss your Self Assessment requirements.
