Self Assessment Deadlines 2025/26: Key Dates You Can’t Miss

Missing a Self Assessment deadline can be expensive. HMRC charges an automatic £100 penalty the moment you file even one day late, and the fines escalate sharply from there. Whether you are employed with additional income, a landlord, or running your own business, knowing the key dates for the 2025/26 tax year is essential to staying on the right side of HMRC.

Who Needs to File a Self Assessment Return?

You must file a Self Assessment tax return if any of the following apply to you:

• You are self-employed as a sole trader and earned more than £1,000
• You are a partner in a business partnership
• You earned more than £150,000 in total income
• You had untaxed income such as rental income, tips, or commission
• You are a company director (unless it was a non-profit with no pay or benefits)
• You or your partner received the High Income Child Benefit Charge
• You received income from abroad that you need to pay UK tax on
• You had capital gains above the annual exempt amount (£3,000 for 2025/26)
• You received dividends above the £500 dividend allowance

The Key Deadlines for 2025/26

5 October 2026 — Register for Self Assessment

If this is your first Self Assessment return, you must register with HMRC by 5 October 2026. For sole traders, this means registering for Self Assessment and Class 2 National Insurance. You will receive a Unique Taxpayer Reference (UTR) number, which can take several weeks to arrive. Do not leave this to the last minute; applying in the summer after the tax year ends is good practice.

31 October 2026 — Paper Filing Deadline

If you still prefer to submit a paper return, your completed form must reach HMRC by 31 October 2026. Paper filing is increasingly rare and we strongly recommend filing online for speed, accuracy, and immediate confirmation of receipt. If you miss this date, you will need to file online by 31 January instead.

30 December 2026 — PAYE Coding Deadline

If you owe less than £3,000 in tax and file your return online by 30 December 2026, HMRC can collect the amount owed through your PAYE tax code the following year. This means no lump-sum payment in January. This option is only available for relatively small amounts and you must file early enough for HMRC to adjust your tax code.

31 January 2027 — Online Filing and Payment Deadline

This is the big one. Your online Self Assessment return and any tax owed must reach HMRC by midnight on 31 January 2027. This includes:

• Your balancing payment for the 2025/26 tax year
• Your first payment on account for 2026/27 (if applicable)

31 July 2027 — Second Payment on Account

If you are required to make payments on account, your second instalment for the 2026/27 tax year is due by 31 July 2027. Payments on account apply when your previous tax bill was more than £1,000 and less than 80% was collected through PAYE. Each payment on account is typically half of your previous year’s tax bill.

What Happens If You Miss a Deadline?

Late Filing Penalties

• 1 day late: Automatic £100 penalty (even if you owe no tax)
• 3 months late: £10 per day for up to 90 days (maximum £900)
• 6 months late: £300 or 5% of the tax due, whichever is greater
• 12 months late: A further £300 or 5% of tax due; in serious cases, up to 100% of the tax due

Late Payment Penalties

If you do not pay your tax by 31 January:

• 30 days late: 5% of the tax unpaid at that date
• 6 months late: A further 5% of the amount still outstanding
• 12 months late: An additional 5% on top

HMRC also charges interest on late payments, currently at the Bank of England base rate plus 2.5%. This runs from the date the payment was due until the date you pay.

How to Avoid Penalties

1. Set calendar reminders for every key date listed above
2. Register early — waiting for your UTR number is the most common cause of missed deadlines
3. File early — you can submit your return from 6 April 2026 onwards; filing early does not mean paying early
4. Keep records throughout the year — scrambling for receipts in January leads to errors and delays
5. Use an accountant — a professional ensures accuracy and files on time; their fees are tax-deductible for the self-employed

Filing early gives you more time to budget for any tax owed. You do not have to pay until 31 January regardless of when you file, but knowing the amount months in advance is far less stressful than a surprise bill on the deadline.

Need Help With Your Self Assessment?

At HS Global Accountancy, we handle the entire Self Assessment process for you. From registering with HMRC to filing your return and calculating your payments on account, we ensure everything is accurate and submitted on time. Our core accounting services cover Self Assessment for individuals, sole traders, landlords, and company directors.

If you have questions about your obligations or want to hand the whole process to a professional, get in touch today.