How to File Your 2025 to 2026 Self Assessment Tax Return Online With HMRC

Check whether you need to file Self Assessment

Self Assessment is used to report income, gains and other information that HMRC cannot fully deal with through PAYE or another tax mechanism. For the tax year from 6 April 2025 to 5 April 2026, HMRC says you must file in several situations, including if you were a sole trader with more than £1,000 of gross trading income, were a partner in a partnership, had Capital Gains Tax to pay, or had a High Income Child Benefit Charge that was not being collected through PAYE.

A return may also be needed for untaxed income such as rent from property or land, tips and commission, savings interest, dividends, foreign income or taxable UK income received by a non-UK resident. If you are unsure, use HMRC's official eligibility checker before registering.

Register with HMRC before filing for the first time

If you need a return for 2025 to 2026 and have not sent one before, you must normally tell HM Revenue & Customs (HMRC) by 5 October 2026. The same check applies if you previously registered but did not need to send a return for 2024 to 2025, because you may need to reactivate your Self Assessment account.

HMRC will give you a 10-digit UTR when you register. If you are not self-employed and need to register for another Self Assessment reason, HMRC uses form SA1. HMRC says it usually contacts people registering through SA1 within 21 days, although it can take longer during busy periods.

If you register after 5 October 2026, HMRC may give you a filing deadline that is three months from the date of its letter or email. However, the tax payment deadline remains 31 January 2027, so late registration should not be treated as extra time to pay.

Gather the records you need before starting

HMRC requires you to keep records so that your return is complete and accurate. Depending on your circumstances, useful records include:

• your National Insurance number and UTR;
• P60, P45 or P11D information for employment income and benefits;
• bank statements and records of untaxed interest or other income;
• self-employment invoices, receipts, income and allowable expense records;
• rental income and property expense records;
• pension statements;
• records of disposals that produced capital gains;
• details of overseas income; and
• evidence for reliefs you claim, such as qualifying pension contributions or Gift Aid donations.

Your personal tax account or HMRC app may already show some of your tax information, but you remain responsible for checking that your return is accurate.

File the return using HMRC's online service

For most individual taxpayers, HMRC provides an online Self Assessment service. You can file a 2025 to 2026 return from 6 April 2026 and do not have to complete it in one session because the service allows you to save your work and return later.

1. Sign in to HMRC's online Self Assessment service.
2. Enter your UTR when required.
3. Complete any identity verification HMRC requests.
4. Answer the questions about your circumstances so the appropriate sections of the return are completed.
5. Enter your income, expenses, gains, tax already paid and applicable reliefs.
6. Review the tax calculation and your entries.
7. Submit the return and retain confirmation of submission.

The HMRC online service can also show previous returns, your details, how much you owe and your tax calculation.

When the standard HMRC online service is not suitable

HMRC's standard individual online filing service cannot be used for certain returns, including partnership returns, trusts or estates, returns for people who lived abroad as non-residents, and some specialist income or gains situations. HMRC directs affected taxpayers to commercial software or the appropriate forms. Do not assume that submitting an ordinary individual return through the standard service is valid for one of these specialist cases.

Meet the 31 January 2027 online deadline

The key deadlines for the 2025 to 2026 tax year are:

• 5 October 2026 — normally tell HMRC you need to file if you are a new filer or need to reactivate.
• 31 October 2026 at 11:59pm — HMRC must receive a standard paper return by this deadline.
• 30 December 2026 at 11:59pm — submit by this date if you want HMRC to consider collecting an eligible Self Assessment bill through your tax code.
• 31 January 2027 at 11:59pm — deadline for the online return.
• 31 January 2027 at 11:59pm — deadline for the tax due for the year.

If you are required to make payments on account, these are normally paid in two instalments, due on 31 January and 31 July. Payments on account generally do not apply if the previous year's Self Assessment tax was less than £1,000 or if more than 80% of the tax was already collected outside Self Assessment.

What happens if you file or pay late

If a return is required and you miss the filing deadline, the current Self Assessment late-filing regime starts with an £100 penalty. After three months, HMRC can charge daily penalties of £10 for up to 90 days. At six months and again at 12 months, further penalties can apply, generally 5% of the tax due or £300, whichever is greater.

Late payment can also lead to penalties and interest. HMRC states that late-payment penalties can be charged at 30 days, six months and 12 months. If you have missed a deadline, file and pay as soon as possible rather than waiting for HMRC to contact you.

If some figures are not final by the deadline

Not having every final figure does not automatically allow you to miss the filing deadline. HMRC permits provisional figures where, for example, the final profit cannot yet be established. You should identify the figures as provisional when filing and amend the return when the final information becomes available.

HMRC normally allows you to amend the return for up to 12 months after the Self Assessment deadline. Additional tax arising from corrected provisional figures can attract interest from the original payment due date.

Know whether Making Tax Digital changes how you file

Making Tax Digital for Income Tax starts from 6 April 2026 for qualifying self-employed people and landlords whose qualifying income is over £50,000, subject to the detailed eligibility and exemption rules. However, HMRC specifically states that people entering Making Tax Digital must still submit their 2025 to 2026 Self Assessment return in the normal way. The Making Tax Digital software filing requirement applies to subsequent digital-obligation tax years.

If you are required to use Making Tax Digital for 2026 to 2027, you must use compatible software for the relevant digital records, quarterly updates and tax return rather than treating the ordinary HMRC Self Assessment web form as a substitute.

Avoid problems that can delay or invalidate your return

• Do not wait until January to register if you are a first-time filer; you need your Self Assessment registration and UTR.
• Do not assume that filing the return also pays the tax bill. Filing and payment are separate obligations.
• Do not omit income merely because tax was not deducted when you received it.
• Do not use the standard HMRC individual online service if your type of return requires commercial software or another filing route.
• Check that an online submission has actually been accepted and keep confirmation.
• If you use provisional figures, identify them and correct the return once final figures are available.

After submitting your return

HMRC's online service shows the calculation based on the figures you report and lets you check how much Self Assessment tax you owe. Keep your submission confirmation and supporting records. Pay the amount due by the applicable deadline and check whether your account also shows a first payment on account for the following tax year.

If you discover an error after filing, you can normally amend an online Self Assessment return within the permitted amendment period. If HMRC issues a late filing or late payment penalty and you believe you have a reasonable excuse, there is an official appeal process.