Self Assessment 2026: Deadlines, Who Must File & Penalties

The online self assessment deadline 2026 is midnight on 31 January 2026 for the 2024/25 tax year. Miss it and HMRC charges an automatic £100 penalty — even if you have no tax to pay. Self Assessment is how millions of people in the UK report income that is not taxed at source, and the rules around dates, who must file and penalties trip up new and experienced filers alike every year.

This guide sets out the key dates in plain English, explains exactly who needs to file, shows how late penalties stack up with a worked example, and points you to our self assessment service if you would rather hand the whole thing over.

The key self assessment deadlines for 2026

Self Assessment runs on a fixed annual cycle tied to the UK tax year, which ends on 5 April. The return you file by 31 January 2026 covers the 2024/25 tax year (6 April 2024 to 5 April 2025). Here are the dates that matter:

Deadline	Date	What it is for
Register for Self Assessment	5 October 2025	First-time filers must tell HMRC they need to file by 5 October following the end of the tax year
Paper tax return	31 October 2025 (midnight)	Deadline if you file on paper rather than online
Online tax return	31 January 2026 (midnight)	Deadline to file your return electronically
Pay the tax you owe	31 January 2026 (midnight)	Balancing payment for 2024/25 due the same day
First payment on account	31 January 2026	Advance instalment towards 2025/26 (if applicable)
Second payment on account	31 July 2026	Second advance instalment towards 2025/26

The single date most people remember is 31 January — that is both the online filing deadline and the payment deadline. They fall on the same day, so do not assume you have longer to pay once you have filed. Always confirm current dates on GOV.UK, as deadlines occasionally shift and figures are reviewed each year.

Why registering by 5 October matters

If you have never filed before — say you started self-employment or became a landlord during 2024/25 — you must register for Self Assessment by 5 October 2025. Registration gives you a Unique Taxpayer Reference (UTR) and lets you set up an online account. Leave it late and you may not get your UTR and activation code in time to file by 31 January, and HMRC can charge a “failure to notify” penalty based on the tax you owe.

Paper versus online

The paper deadline of 31 October is three months earlier than the online one. Most people now file online, which gives you until 31 January and calculates your tax automatically as you go. Paper filing still exists, but unless you have a specific reason for it, online is simpler and gives you the longer window.

Payments on account explained

If your Self Assessment bill is more than £1,000 (and less than 80% of your tax was collected at source), HMRC asks you to make payments on account towards next year’s bill. These are two advance instalments, each equal to half of your previous year’s tax liability:

• The first payment on account is due by 31 January alongside your balancing payment.
• The second payment on account is due by 31 July.

When you file the following year’s return, your actual bill is compared with what you paid on account, and you either pay the difference (a “balancing payment”) or get the overpayment back. This is why a first tax bill can feel unexpectedly large — you may be paying the year’s tax plus a 50% advance for next year, all on 31 January.

Who needs to file a self assessment tax return?

You must complete a Self Assessment tax return if, in the tax year, any of the following applied to you. This list is not exhaustive — check GOV.UK or ask an accountant if you are unsure — but it covers the most common cases.

Self-employed and sole traders

If you were self-employed as a sole trader and earned more than £1,000 (before deducting expenses), you must register and file. This is the most common trigger. It applies to freelancers, tradespeople, consultants, online sellers, gig-economy and side-hustle income — anything where you work for yourself rather than through PAYE.

Landlords

If you receive rental income from property — a buy-to-let, a room, a holiday let, or land — and your gross property income is above £1,000, you generally need to file. Property income has its own rules around allowable expenses, mortgage interest relief and the property allowance, so it pays to get it right. Our accountant for landlords page explains how we handle property tax returns.

Company directors with untaxed income

Being a company director does not automatically require a return, but most directors do file because they receive dividends or other untaxed income alongside their salary. If you take dividends from your own limited company, you will almost certainly need to report them.

High earners and the High Income Child Benefit Charge

You will usually need to file if your income is high enough to trigger the High Income Child Benefit Charge — broadly where you or your partner have adjusted net income over £60,000 and someone in the household claims Child Benefit. Very high earners (with income over £150,000 in recent years) have also been brought into Self Assessment, and tapering of the personal allowance above £100,000 commonly requires a return.

People with significant savings, dividends or capital gains

You may need to file if you have:

• Savings interest above your Personal Savings Allowance that HMRC cannot collect through your tax code.
• Dividend income above the (now small) dividend allowance.
• Capital gains above the annual exempt amount, for example from selling shares or a second property. See our guide to the capital gains tax allowance for the current figures and how gains are taxed.

Untaxed foreign income and other cases

Other triggers include untaxed foreign income, income from a trust or estate, certain pension scheme charges, and being a partner in a business partnership. If you receive income that has not already had the right amount of tax taken off, Self Assessment is usually how HMRC collects it.

The £1,000 trading allowance

The trading allowance lets you earn up to £1,000 of gross trading or miscellaneous income in a tax year completely tax-free, with no need to report it. There is an equivalent property allowance of £1,000 for rental income.

If your income is below £1,000, you generally do not need to register or file at all. If it is above £1,000, you must declare it — but you can choose to deduct the £1,000 allowance instead of your actual expenses, whichever gives you the better result. For someone with very low costs (an online seller, say), claiming the flat £1,000 can be simpler and more generous than itemising real expenses.

Late-filing and late-payment penalties

HMRC’s penalty regime for missing the 31 January deadline is strict and escalates quickly. Filing late and paying late are penalised separately, and interest is charged on top.

Late filing penalties:

• £100 immediately the day after the deadline — automatic, and charged even if you owe no tax or are due a refund.
• Daily penalties of £10 once the return is 3 months late, for up to 90 days — a maximum of £900.
• At 6 months late, a further penalty of 5% of the tax due or £300, whichever is higher.
• At 12 months late, another 5% of the tax due or £300, whichever is higher.

Late payment penalties (on tax paid late):

• 5% of the unpaid tax at 30 days late.
• A further 5% at 6 months.
• Another 5% at 12 months.
• Interest accrues daily on overdue tax from 1 February until you pay, at HMRC’s published rate.

Worked example: how late penalties stack up

Imagine you owe £2,000 in tax for 2024/25 and simply forget to file. Here is how the late-filing penalties alone build up over the year:

1 day late (1 Feb)            £100   fixed penalty
3 months late (from ~1 May)   £900   daily £10 × 90 days
6 months late (1 Aug)         £300   higher of 5% (£100) or £300
12 months late (1 Feb 2027)   £300   higher of 5% (£100) or £300
                            ------
Total late-filing penalties  £1,600

On top of that £1,600, you would face late-payment penalties (5% of £2,000 = £100 at each of 30 days, 6 months and 12 months, so £300 more) plus interest on the unpaid £2,000 running from 1 February. In this example the penalties and interest alone approach the size of the original tax bill — which is why filing on time matters even if you cannot immediately pay.

If you genuinely cannot pay, it is far better to file on time and arrange a Time to Pay plan with HMRC than to miss the deadline. Filing stops the larger filing penalties even when payment is delayed.

Making Tax Digital for Income Tax from April 2026

A significant change is arriving: Making Tax Digital (MTD) for Income Tax begins to roll out from April 2026. In the first phase, it applies to self-employed people and landlords with qualifying income over £50,000. Affected taxpayers will need to keep digital records and send quarterly updates to HMRC using compatible software, replacing the single annual return for those in scope.

The threshold is expected to fall to £30,000 and then lower in later phases, so most sole traders and landlords will eventually be affected. If you are caught by the first wave, now is the time to get your bookkeeping onto suitable software. Our Making Tax Digital page explains what changes and how we help clients transition smoothly. Check GOV.UK for the latest thresholds and start dates, as the timetable has been revised before.

Tips to make Self Assessment painless

• Register early — do not leave it until January if it is your first return.
• Keep records as you go. Store invoices, receipts and bank statements throughout the year rather than scrambling in January.
• Set money aside. A rough rule for the self-employed is to put away 20–30% of profit for tax and National Insurance.
• Claim all allowable expenses — or the trading/property allowance if it is better.
• File well before 31 January to avoid the website rush and to know your bill in advance.

Get help with your self assessment

Self Assessment is manageable, but the rules around what to report, which expenses you can claim and which deadlines apply can be genuinely confusing — and the penalties for getting it wrong are steep. Yes, an accountant can file your self assessment for you: we register as your HMRC agent, prepare and check the return, make sure you claim everything you are entitled to, and submit it on time.

We work with the self-employed, landlords, company directors and high earners across Surrey and beyond, including as a local accountant in Reigate. Whether you want us to handle the whole return or just check your figures before you file, we can help.

Book a free consultation to discuss your Self Assessment, or read more about our self assessment service.

For the official rules and to file your return, see GOV.UK: Self Assessment tax returns.