Self Assessment checklist for the 31 January 2027 deadline

Who must file a 2025/26 tax return

You need to send a Self Assessment return for 2025/26 if, between 6 April 2025 and 5 April 2026, any of these applied to you:

• You were self-employed as a sole trader and your income was more than £1,000 before taking off expenses. The £1,000 is the trading allowance.
• You were a partner in a business partnership.
• You owe Capital Gains Tax, for example after selling shares or a second home at a profit.
• You have to pay the High Income Child Benefit Charge (you or your partner got Child Benefit, your income was over £60,000 and you are the higher earner) and you do not pay it through your tax code.
• You had untaxed income HMRC needs to know about, such as rent from a property, tips and commission, or savings, dividend or foreign income.
• HMRC wrote to you asking you to send a return. If you think you no longer need to, tell HMRC rather than ignoring the letter.

Not sure? HMRC has a short online checker. If you have never filed before and need to for 2025/26, the deadline to register was 5 October 2026. If you missed it, register now: your Unique Taxpayer Reference (UTR) is sent by post and you need it before you can file online.

Key dates for the 2025/26 return

Penalties if you are late

Filing late and paying late are separate penalties, so file on time even if you cannot pay in full yet.

If you pay late, HMRC adds 5% of the unpaid tax at 30 days, again at 6 months and again at 12 months, and charges interest on everything owed. If you cannot pay, contact HMRC about a payment plan before the deadline.

Records to gather

Work through the list and tick off what applies to you. Every figure is for 6 April 2025 to 5 April 2026.

About you

• Your UTR, National Insurance number and the sign-in details for your HMRC online account.
• Last year's return, and the payments on account you made in January and July 2026, if any.

Jobs and pensions

• Your P60 from each employer, and your P45 if you left a job during the year.
• Your P11D if you had benefits such as a company car or medical insurance.
• Pension income: P60s from pension providers and the State Pension you received.

Self-employment and side income

• Total takings, and expenses sorted into HMRC's categories (see the sole trader expenses guide).
• Your business mileage log, if you claim the flat mileage rate. For 2025/26 that is 45p a mile for the first 10,000 miles in a car or van.
• Whether the £1,000 trading allowance beats your actual costs: the side hustle guide has a calculator.

Property

• Rent received, letting costs and repair invoices for each property.
• Your mortgage interest statement: interest is not deducted from rent but gives a 20% tax credit (see the landlord expenses guide).

Savings, investments and gains

• Interest statements from banks and building societies (not ISAs), and dividend vouchers.
• For anything you sold at a gain, such as shares or a second home: the dates, the price you paid and sold for, and the costs of buying and selling.

Reliefs you can claim

• Personal pension contributions and Gift Aid donations, which can give higher-rate taxpayers extra relief.
• Child Benefit received, if the High Income Child Benefit Charge applies.
• Your student loan plan, if you have one.

How to file, step by step

1. Check you need to file with HMRC's checker, and register if this is your first year.
2. Sign in to your HMRC online account and start your 2025/26 return. Allow time: first-time sign-in can need identity checks.
3. Gather your records using the list above, totalled for 6 April 2025 to 5 April 2026.
4. Fill in each section that applies: employment, self-employment, property, savings, gains and reliefs. HMRC works out the tax as you go.
5. Check the calculation before you submit. Look at the payments on account it shows for 2026/27.
6. Submit by 31 January 2027 and keep the submission reference HMRC gives you.
7. Pay by 31 January 2027. GOV.UK lists the ways to pay; bank transfers can take a few days, so do not leave it to the last day.
8. Keep your records. If you are self-employed, keep them for at least 5 years after the 31 January deadline: for the 2025/26 return, until at least the end of January 2032.

Payments on account, with an example

Payments on account are advance payments towards next year's bill. Each one is half of last year's tax, and they are due on 31 January and 31 July. You do not have to make them if last year's Self Assessment bill was under £1,000, or if more than 80% of your tax was already taken through your tax code or deducted at source.

The first year catches people out, because the January bill includes both the whole of last year's tax and the first advance payment for this year.

Worked example: a first return

Alex starts a small business alongside a job. Their 2025/26 return shows £2,400 of tax and Class 4 National Insurance to pay, and none of it was taken through their tax code.

If you expect your profits to fall, you can ask HMRC to reduce your payments on account, online or on form SA303. If you reduce them too far, HMRC charges interest on the shortfall.

The Sole Trader Bookkeeping spreadsheet shows whether payments on account apply and exactly what is due on each date, and the Side Hustle Tracker does the same for smaller side incomes.

Sources

Every rate and rule on this page was checked on GOV.UK on 8 November 2026.

• Self Assessment tax returns: deadlines
• Self Assessment: who must send a tax return
• Self Assessment: penalties
• Understand your Self Assessment bill: payments on account
• High Income Child Benefit Charge
• Simplified expenses: vehicles (mileage rates)
• How long to keep your records (self-employed)
• Check if you need to send a tax return

Planning tool, not tax advice. This guide explains the general GOV.UK rules in plain English. Your own position can differ: check GOV.UK, ask HMRC, or speak to an accountant if you are unsure.