Self Assessment Deadline 2026: Key Dates for the 2025/26 Tax Year

The Key Dates at a Glance

The 2025/26 tax year runs from 6 April 2025 to 5 April 2026. Here are the critical Self Assessment deadlines you need to be aware of:

• 5 October 2026: Deadline to register for Self Assessment if you became self-employed or started receiving untaxed income during 2025/26 and have not previously registered
• 31 October 2026: Deadline for filing a paper Self Assessment tax return (rarely used now, but still available)
• 30 December 2026: Deadline for filing online if you want HMRC to collect tax owed (under £3,000) through your PAYE tax code for the following year
• 31 January 2027: Deadline for filing your online Self Assessment tax return for 2025/26
• 31 January 2027: Deadline for paying the balancing payment for 2025/26 and the first payment on account for 2026/27
• 31 July 2027: Deadline for the second payment on account for 2026/27

Who Needs to File a Self Assessment Return?

You must file a Self Assessment tax return for 2025/26 if any of the following apply:

• You were self-employed and your gross income exceeded £1,000 (the trading allowance)
• You were a partner in a business partnership
• You received rental income from property
• You had untaxed income (e.g., from investments, overseas sources, or tips) exceeding £2,500
• You or your partner received Child Benefit and your individual income exceeded £60,000 (the High Income Child Benefit Charge threshold, increased from £50,000 in 2024/25)
• You had capital gains above the Annual Exempt Amount (£3,000 for 2025/26)
• You were a company director (unless you were a director of a non-profit organisation and received no pay or benefits)
• Your total taxable income exceeded £150,000
• You received a P800 from HMRC indicating tax is owed that cannot be collected through your tax code

If you are unsure whether you need to file, our Self Assessment team can advise you quickly and avoid any risk of penalties for non-filing.

How to Register for Self Assessment

If you are new to Self Assessment and need to register for the first time, you must do so by 5 October 2026. This applies if you became self-employed, started receiving rental income, or had any other reason to file a return during the 2025/26 tax year. To register, you need to complete form SA1 (or CWF1 if you are self-employed) on GOV.UK. HMRC will then issue you a Unique Taxpayer Reference (UTR), which you will need to file your return. Registration can take several weeks, so do not leave it until the last minute.

The 31 January Deadline: Why It Matters Most

The 31 January 2027 deadline is the most important date in the Self Assessment calendar. It is both the filing deadline for your 2025/26 online tax return and the payment deadline for any tax you owe. Missing this date triggers multiple consequences: an automatic £100 late-filing penalty (even if you owe no tax or have already paid), interest on any unpaid tax from 1 February 2027, and a late-payment penalty if the tax remains unpaid after 30 days. The interest rate HMRC charges is currently 7.25%, significantly higher than most savings accounts pay, so there is a real financial cost to paying late.

Penalties for Late Filing

HMRC's penalty regime for late Self Assessment returns escalates over time:

• 1 day late: £100 fixed penalty (applies even if no tax is due)
• 3 months late: £10 per day, up to a maximum of £900 (in addition to the initial £100)
• 6 months late: The greater of 5% of the tax due or £300 (in addition to penalties above)
• 12 months late: A further 5% of the tax due or £300, whichever is greater. In serious cases, HMRC can charge up to 100% of the tax due

These penalties add up quickly. A return that is 12 months late could attract penalties of £1,600 or more, plus interest on the unpaid tax. If you have a reasonable excuse for filing late, such as serious illness or an HMRC system failure, you can appeal the penalty within 30 days of the penalty notice.

Payments on Account Explained

If your Self Assessment tax bill is more than £1,000, and less than 80% of your total tax liability was collected at source (through PAYE), you will need to make payments on account. These are advance payments towards the following year's tax bill, each equal to 50% of your current year's liability. The first payment on account is due on 31 January 2027 (at the same time as the balancing payment for 2025/26), and the second is due on 31 July 2027.

This means that on 31 January 2027, you may need to pay both the balance of your 2025/26 tax and the first instalment towards 2026/27 — a potentially large combined payment. Planning ahead is essential. Use our tax calculator to estimate your liability and start setting money aside throughout the year.

If your income drops significantly, you can apply to reduce your payments on account through your online Self Assessment account. Be careful not to reduce them too far: if your final bill is higher, HMRC charges interest on the shortfall.

What If You Cannot Pay on Time?

If you cannot pay your tax bill by 31 January, do not ignore the problem. HMRC offers a "Time to Pay" arrangement that allows you to spread your payment over up to 12 months. You can set this up online if your tax bill is £30,000 or less and you are within 60 days of the payment deadline. For larger amounts, you will need to call HMRC directly. Interest will still be charged on the outstanding balance, but you will avoid the late-payment surcharges. The key is to act proactively — HMRC is far more accommodating if you contact them before the deadline rather than after.

How to File Early and Avoid the Rush

While the deadline is 31 January 2027, there is no rule that says you have to wait until then. You can file your 2025/26 return as soon as the tax year ends on 5 April 2026 (HMRC's online system for 2025/26 returns typically opens in April or May 2026). Filing early has several advantages:

• You know your tax liability months in advance, giving you time to save
• If you are due a refund, you receive it sooner
• You avoid the stress and rush of the January filing season
• You can spread your payments on account more manageably
• Your accountant has more time to review your return thoroughly and identify all available deductions

Filing early does not mean you pay early. Even if you file in May 2026, the tax is still not due until 31 January 2027 (unless you choose to pay sooner).

What You Need to File Your Return

Gather the following information before starting your return: your UTR and National Insurance number, P60 and P11D from your employer (if applicable), bank interest certificates, dividend vouchers, records of all self-employment income and expenses, rental income and expenses, pension contributions, Gift Aid donations, student loan details, and any foreign income. Having everything ready before you start will make the process much quicker and reduce the risk of errors.

Changes to Watch for 2025/26

Several changes affect Self Assessment for the 2025/26 tax year that you should be aware of:

• Making Tax Digital for ITSA: From April 2026, self-employed individuals and landlords with gross income above £50,000 must keep digital records and submit quarterly updates. This runs in parallel with the annual Self Assessment return for now.
• High Income Child Benefit Charge: The threshold has increased to £60,000, and the taper now runs to £80,000 (previously £50,000 to £60,000). If you previously had to repay Child Benefit and your income is between £50,000 and £60,000, you may no longer need to.
• Capital Gains Tax rates: The lower rate for basic-rate taxpayers increased to 18% and the higher rate to 24% from October 2024, applying to disposals in 2025/26.
• National Insurance: Class 4 NIC rates for the self-employed are 6% (main rate) and 2% (higher rate) for 2025/26.

Get Help With Your Return

Filing your Self Assessment return accurately and on time is essential, but it does not have to be stressful. Our Self Assessment service takes the entire process off your hands — we gather your information, identify all allowable deductions, prepare and file your return, and calculate your tax liability with precision. We also send you reminders well before each deadline so you are never caught out.

Whether you are a sole trader, freelancer, landlord, company director, or high-income individual, we ensure your return is complete, accurate, and filed on time. Get a quote today, or contact us to book your free consultation before the January rush begins.