Self Assessment deadline: what to get ready before 31 January 2027
Every January, HMRC receives millions of returns in the final week, and a good share of the mistakes, penalties and overpayments that follow come from the rush rather than the rules. Here is how to make the 2025/26 return a formality.
The dates for the 2025/26 tax year
- 5 October 2026: register for Self Assessment if this is your first year with untaxed income.
- 31 October 2026: paper returns.
- 30 December 2026: file online by this date if you owe less than £3,000 and want it collected through your PAYE tax code over the following year.
- 31 January 2027: online filing deadline, payment of the balance for 2025/26, and the first payment on account towards 2026/27.
- 31 July 2027: second payment on account.
What to gather
Most of the delay in preparing a return is hunting for paperwork, not working out the tax. Pull these together now:
- P60s and P45s from any employment, plus P11Ds for benefits
- Self-employment income and expenses for the year, ideally straight from your accounting software
- Rental income and allowable property costs, with mortgage interest statements
- Dividend vouchers, including dividends from your own company
- Bank and building society interest, and any other investment income
- Pension contributions and Gift Aid donations, which can reduce the bill
- Student loan plan type, and whether Child Benefit was received in a household where someone earned over £60,000
- Details of any assets sold: property, shares or crypto
Payments on account: budget for them now
If your last bill was over £1,000 and less than 80% of your tax was collected at source, HMRC expects two advance payments towards the next year, each half of the previous bill. In January that means paying the balance for 2025/26 and the first instalment for 2026/27 on the same day. Knowing the figure in October rather than January is the single biggest stress reducer the system offers, and it is only available to people whose records are ready early.
If Making Tax Digital now applies to you
Sole traders and landlords with qualifying income over £50,000 have been sending quarterly updates since April 2026. The 2025/26 return is still filed the traditional way; from 2026/27 the quarterly updates feed a final declaration, due by the same 31 January date. The two systems overlap this winter, so if you are in both, keep them straight. Our note on MTD quarter by quarter explains the new rhythm.
What a late return costs
Filing late brings an automatic £100 penalty even if no tax is due, with daily penalties after three months. Paying late adds interest from 1 February and a 5% surcharge once the balance is 30 days overdue, with further surcharges at six and twelve months. None of it is deductible, and all of it is avoidable.
Do it in November
A return prepared in November gives you two months' notice of the bill, time to check anything unusual, and the option to spread the payment. A return prepared on 30 January gives you none of those things and the same tax to pay. If your records need work before the return can be done, that is exactly the conversation to have now rather than in the new year.
This note is general guidance, not advice on your circumstances. We prepare and file Self Assessment returns for sole traders, landlords and directors; get in touch and we will tell you what we need.
Published 7 October 2026.