Self Assessment deadline 2027: a 31 January checklist

Last updated: 29 October 2026

Every January someone sits down on the 29th to “just quickly do the tax return”, then finds they can’t sign in, can’t find their UTR, and can’t remember where the bank interest letter went. Most of the stress isn’t the tax. It’s the admin, left until there’s no slack.

Here’s the checklist to get it done calmly, a calculator for what lateness would cost, and the part nobody warns you about: the July payment on account.

When is the Self Assessment deadline for 2025/26?

The 2025/26 tax year ran from 6 April 2025 to 5 April 2026. The dates that matter, from gov.uk:

• 5 October 2026: the deadline to register if you were filing for the first time (or hadn’t filed for 2024/25). If you missed it, HMRC sends a later filing deadline, but the tax is still due on 31 January.
• 31 October 2026: paper returns had to reach HMRC by 11:59pm. If you missed that, you can still file online without penalty.
• 30 December 2026: file online by 11:59pm if you want a bill under £3,000 collected through your tax code instead of in one go. You have to already pay tax through PAYE, as an employee or on a pension.
• 31 January 2027: online return in, and all tax for 2025/26 paid, by 11:59pm. Any first payment on account for 2026/27 is due the same day.
• 31 July 2027: second payment on account, if you have them.

Your 31 January checklist

Work through this in order. The first two steps are the ones that need time, because the fixes can involve post.

1. Check you can sign in. Go to the Self Assessment page on gov.uk and sign in to your HMRC online account. If you can’t, start the recovery now. HMRC may ask you to prove your identity, usually with photo ID.
2. Find your UTR. Your 10-digit Unique Taxpayer Reference is in your HMRC online account, the HMRC app, and on past returns and HMRC letters. If you’ve only just registered, HMRC says it usually arrives by post about 15 days later.
3. Gather your records. Your P60 (and any P45 or P11D) for employment; pension statements; bank and building society interest; dividends; rental income and costs; self-employed income and expenses; pension contributions and Gift Aid donations you want relief for; and anything you sold that might have a capital gain.
4. File the return. Online through your HMRC account, or through software (more below). The return works out your tax for you as you go.
5. Read your calculation. Note the total, and whether it shows a payment on account for next year. That decides how much you need for 31 January, and for 31 July.
6. Pay, or arrange to pay. Pay early enough for the method you’re using (timings below). If you can’t pay in full, file anyway and set up a payment plan.

If you sell online, our guide to Vinted and eBay tax sets out when side sales need to go on a return at all. Most decluttering doesn’t.

What a late tax return actually costs

There are two separate sets of charges. One for filing late, one for paying late, and they stack.

Filing late (from gov.uk’s penalty page):

• £100 the day after the deadline. This applies even if you owe no tax, or have already paid.
• £10 a day once the return is three months late (from 1 May 2027), for up to 90 days: £900.
• At six months late, a further 5% of the tax due or £300, whichever is more.
• At twelve months late, the same again.

The 5% is worked out on the year’s tax bill, and HMRC’s manual says it isn’t reduced by anything you’ve already paid. So a return filed a year late can cost £1,600 in filing penalties even if the tax bill is nil.

Paying late:

• 5% of the tax still unpaid 30 days after the deadline, again at six months, and again at twelve months.
• Interest on everything late, from the day after it was due. HMRC’s late payment rate is Bank Rate plus 4%, which has been 7.75% a year since 9 January 2026, after the Bank of England cut Bank Rate to 3.75% in December 2025. Interest is charged on payments on account too, but the 5% penalties aren’t.

The one thing not to miss: filing and paying are separate. If you can’t pay, file on time anyway. That avoids the £100 and the daily penalties, and lets you set up a payment plan, which you can’t do until your return is in.

You may have read about HMRC’s new points-based penalties, where late payment costs 3% at 15 days and 3% more at 30 days, plus 10% a year. They don’t apply to this return. HMRC says the new rules start from the tax year you join Making Tax Digital for Income Tax, and that “current penalties will apply to your 2025 to 2026 tax return”. From April 2027 they’ll apply to everyone filing a personal return, so next year’s guide will look different. The calculator below uses the current rules.

Payments on account: the July surprise

If your Self Assessment bill is £1,000 or more, HMRC usually asks you to pay towards next year’s bill in advance, in two payments on account, each half of this year’s bill, due on 31 January and 31 July. The exceptions are a bill under £1,000, or more than 80% of your tax already paid at source, through your tax code for example.

Sam’s first year freelancing. Sam went self-employed in 2025, and her 2025/26 return shows a bill of £4,000. She’s never had payments on account. On 31 January 2027 she owes the £4,000 plus a first payment on account of £2,000 for 2026/27: £6,000. On 31 July 2027 she owes another £2,000. It isn’t extra tax, it’s paid early. But £8,000 in six months, against a £4,000 bill, is a shock if you’d only put aside the £4,000.

In year two it evens out, as the payments on account cover most of the next bill. If your income has fallen, you can ask HMRC to reduce your payments on account through your online account (or form SA303). Reduce them too far and you’ll pay interest on the shortfall.

One change on the horizon: the Budget on 28 October 2026 said that from April 2029, people who already make payments on account will pay “smaller, more regular contributions” through the year. The details aren’t out yet, and nothing changes for 2027 or 2028.

Our self-employed money basics guide covers setting money aside from every invoice so January isn’t a scramble.

Three late returns, costed

All three use the 2025/26 rules and today’s 7.75% interest rate, with no tax taken at source.

Mo files and pays six weeks late. His bill is £1,200, so he also has a £600 first payment on account due on 31 January. He files and pays everything on 15 March 2027. Filing: £100. Payment: he’s past the 30-day point, so 5% of £1,200 is £60. Interest on £1,800 for 43 days: £16.44. Total: £176.44, almost all of it avoidable by filing on time.

Ella files a year late. Bill £2,000, filed and paid on 10 February 2028. Filing: £100 + £900 daily + £300 + £300 = £1,600 (5% of £2,000 is only £100, so the £300 minimum applies twice). Payment: three lots of 5% = £300. Interest on £3,000 (bill plus first payment on account) for 375 days: £238.87. Total: about £2,139, more than her tax bill, plus interest on the July payment on account if that’s late too.

Raj owes £800 and pays a month late. No payments on account (he’s under £1,000). Filed on time, paid on 3 March 2027: 5% of £800 is £40, plus about £5.27 interest. Paying one day earlier, on 2 March, would have avoided the £40.

How to pay HMRC

Your payment reference is your 10-digit UTR followed by the letter K. Your bill tells you which HMRC bank account to use, and gov.uk lists both. Allow time for the method:

• Same or next day: online or telephone banking (Faster Payments), CHAPS, card online, or at your bank.
• 3 working days: Bacs, or a Direct Debit you’ve already set up.
• 5 working days: a new Direct Debit.

The Post Office no longer takes HMRC payments, and gov.uk warns online services can be slow at busy times, which means the last week of January. You can also pay in weekly or monthly instalments ahead of the deadline.

Can’t pay it all? Time to Pay

If you can’t pay in full by 31 January, HMRC’s Time to Pay lets you spread the bill over monthly instalments. HMRC says bills up to £30,000 can be set up online without calling, once your return is filed. For bigger amounts, or if you need longer, you can still apply but need to phone. HMRC checks the plan is affordable, so have your income, regular spending and savings to hand.

Interest still runs on what you owe, but HMRC says a plan helps you avoid late payment penalties. Set it up before the 30-day point if you can. If tax is one of several debts you’re struggling with, free help from StepChange, National Debtline or Citizens Advice is worth a call before you agree anything.

If you’re employed and owe less than £3,000, collection through your tax code (file by 30 December) spreads it over the next year’s pay automatically. Our guide to understanding your tax code explains how that shows up on your payslip.

Missed it? Appealing with a reasonable excuse

If something genuinely stopped you, you can appeal, usually within 30 days of the penalty notice. Follow the notice’s instructions, explain why you were late with dates, and file and pay as soon as the problem ends.

Gov.uk’s examples of a reasonable excuse include a partner or close relative dying shortly before the deadline, an unexpected stay in hospital, a serious illness, your computer or software failing while you were preparing your return, problems with HMRC’s online services, a fire, flood or theft, unforeseeable postal delays, and delays related to a disability or mental health condition.

What doesn’t count: not having the money, finding HMRC’s online system too difficult, not getting a reminder from HMRC, or making a mistake on your return.

Filing it: free first, software if it helps

You don’t need to pay anyone to file. HMRC’s own online service is free and does the sums for you. For most people with a salary, some savings interest or a simple side income, that’s all you need.

Software earns its keep if you’re self-employed or a landlord with lots of transactions: it keeps your records through the year and files from them, which matters more now Making Tax Digital for Income Tax is bringing in digital records and quarterly updates. HMRC publishes a list of compatible software, some of it free.

Three widely used options for sole traders and landlords are FreeAgent, Xero and QuickBooks. Check the plan includes Self Assessment filing, and use any free trial before the January rush rather than during it.

Frequently asked questions

What is the Self Assessment deadline for the 2025/26 tax year?

Online returns and payment by 11:59pm on 31 January 2027. Paper returns were due by 31 October 2026; to pay a bill under £3,000 through your tax code, file online by 30 December 2026.

How much is the penalty for a late tax return?

£100 the day after the deadline, even if you owe nothing; £10 a day from three months late, for up to 90 days; and at six and twelve months, 5% of the tax due or £300, whichever is more.

Do the new points-based penalties apply to my 2025/26 return?

No. HMRC says they start from the tax year you join Making Tax Digital, and the current penalties still apply to the 2025/26 return. From April 2027 they apply to everyone filing a personal return.

What is a payment on account?

An advance payment towards next year’s tax. If your bill is £1,000 or more and less than 80% of your tax was taken at source, HMRC usually asks for two, each half this year’s bill, on 31 January and 31 July.

What interest does HMRC charge on late Self Assessment tax?

Bank Rate plus 4%: 7.75% since 9 January 2026. It’s simple daily interest from the day after the due date until you pay, on payments on account too.

Can I pay my tax bill in instalments?

Yes. Once your return is filed, HMRC says bills up to £30,000 can be spread with a payment plan set up online. For more, or a longer plan, phone HMRC. Interest runs on what’s outstanding.

Want to try other dates or amounts? The late tax return penalty calculator also has its own page, alongside our other free tools.

Just so you know: this guide is information and journalism, not financial advice, and we don't recommend specific financial products. Your circumstances are your own — if you need personal advice, speak to a suitably qualified adviser. Information was correct at the "last updated" date above but things change; always check the linked primary sources.

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