Self Assessment Key Dates and Deadlines 2026/27: Complete Calendar

Missing a Self Assessment deadline is an expensive mistake. HMRC imposes automatic penalties for late registration, late filing, and late payment -- and interest runs on outstanding tax from the due date. Whether you are filing for the first time or have been self-employed for years, keeping a clear record of the key dates for 2026/27 is essential.

Who Needs to File a Self Assessment Return?

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

• You were self-employed (sole trader) with trading income above GBP 1,000
• You were a partner in a business partnership
• You had total untaxed income above GBP 2,500 (for example, rent from property)
• Your savings or investment income exceeded GBP 10,000
• You received income from abroad
• You had capital gains above the Annual Exempt Amount (GBP 3,000 for 2026/27)
• You claimed child benefit and the highest earner in your household had income above GBP 60,000 (HICBC)
• Your total income exceeded GBP 100,000
• You are a company director
• HMRC has issued you a notice to file

If you are unsure whether you need to file, HMRC's online tool can guide you -- or seek advice from a tax professional.

The Key Dates for 2026/27

5 April 2026 -- Tax year end. The 2025/26 tax year closes. All income, expenses, and events within the year from 6 April 2025 to 5 April 2026 will appear on your 2025/26 return.

6 April 2026 -- New tax year begins. The 2026/27 tax year opens. New rates and thresholds apply from this date.

31 July 2026 -- Second payment on account. The second payment on account for 2024/25 is due by 31 July 2026. Payments on account are advance payments toward next year's bill, each equal to 50% of the previous year's tax liability (excluding capital gains). If your 2024/25 liability was GBP 6,000, you paid GBP 3,000 on 31 January 2026 and owe GBP 3,000 on 31 July 2026. Missing this date triggers 3.25% interest (rates set by HMRC and may vary) on the unpaid amount.

5 October 2026 -- Deadline to register for Self Assessment. If you need to file a return for 2025/26 and have not previously been registered, you must notify HMRC by 5 October 2026. Register online at gov.uk via your HMRC account or by calling HMRC. Late registration can result in a penalty equivalent to 30% of the tax due.

31 October 2026 -- Paper return deadline. If you choose to file a paper tax return rather than online, it must reach HMRC by 31 October 2026. Paper returns are increasingly uncommon but remain an option. Note that paper filing gives you less time than online and HMRC cannot acknowledge receipt the same way. For complex returns or certain non-resident situations, paper may still be necessary.

30 December 2026 -- Optional online filing deadline for PAYE coding. If you owe less than GBP 3,000 in tax and are employed or receive a pension, you can ask HMRC to collect the tax through your PAYE code the following year rather than paying it as a lump sum. To do this, you must file your online return by 30 December 2026. This is optional but useful for employed individuals with modest side income.

31 January 2027 -- Main online filing deadline. The online Self Assessment return for 2025/26 must be submitted by midnight on 31 January 2027. Missing this deadline triggers an automatic GBP 100 penalty, even if no tax is owed. A further GBP 10 per day is charged for returns more than three months late (up to 90 days, a maximum of GBP 900). Six months late adds 5% of the tax due or GBP 300 (whichever is higher). Twelve months late adds a further 5% or GBP 300.

31 January 2027 -- Balancing payment for 2025/26. The balancing payment -- the difference between your total 2025/26 tax liability and the payments on account already made -- is due on 31 January 2027. If your payments on account covered the full liability, nothing is owed. If they fell short, pay the difference by this date to avoid interest.

31 January 2027 -- First payment on account for 2026/27. On the same day as your balancing payment, the first payment on account for 2026/27 is due. This is 50% of your 2025/26 liability (unless you apply to reduce it, for example because you expect income to be lower). The two amounts -- balancing payment and first POA -- are combined into a single payment if you pay online.

31 July 2027 -- Second payment on account for 2026/27. The second advance payment for 2026/27, again 50% of the prior year's liability, falls due on 31 July 2027. This date begins the cycle again for the following year.

Reducing Your Payments on Account

If you expect your 2026/27 income to be lower than 2025/26, you can apply to reduce your payments on account. Do this via your HMRC online account or by submitting form SA303. Be cautious: if you reduce too far and your actual liability is higher, you will owe interest on the underpaid amount. HMRC may also enquire into significant reductions.

Penalties at a Glance

• Late filing (online, up to 3 months): GBP 100
• Late filing (3-6 months): GBP 10/day (max GBP 900)
• Late filing (6-12 months): additional 5% of tax or GBP 300
• Late filing (over 12 months): further 5% or GBP 300
• Late payment (30 days+): 5% of unpaid tax
• Late payment (6 months+): further 5%
• Late payment (12 months+): further 5%
• Interest on unpaid amounts runs from the due date

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Use the CalcHub self-employed tax calculator to estimate your 2025/26 liability and calculate how much to set aside for your January 2027 payment.