Guide · Self Assessment
Who Must File Self Assessment 2025/26?
The 2025/26 Self Assessment tax return covers income earned between 6 April 2025 and 5 April 2026. The online filing and payment deadline is 31 January 2027. Around 12 million people in the UK are required to file annually — but many are unsure whether they need to. This guide explains exactly who must file, how to register if you are new to Self Assessment, all the key dates, the new Making Tax Digital ITSA obligations coming from April 2026, and what happens if you file or pay late.
Key Self Assessment dates — 2025/26 tax year
- 5 October 2026: register for Self Assessment if you are new
- 31 October 2026: paper return deadline
- 31 January 2027: online return deadline + pay all tax owed
- 31 July 2027: second payment on account (if applicable)
- Interest on late payment: 7.5%/yr from 1 February 2027
Who Must File a Self Assessment Return for 2025/26?
HMRC requires a Self Assessment return in any of the following circumstances for the 2025/26 tax year:
| Situation | Threshold / condition |
|---|---|
| Self-employed sole trader | Gross trading income above £1,000 |
| Partner in a business partnership | Any level of partnership income |
| Income above £100,000 | Regardless of whether all PAYE |
| Untaxed income | Above £2,500 (dividends, rental, freelance etc.) |
| Capital gains above AEA | Gains above £3,000 annual exempt amount |
| High Income Child Benefit Charge | Either partner's income above £60,000 |
| Foreign income | Any amount of income from outside UK |
| Trust or estate income | Trustee or personal representative income |
| HMRC sends you a notice | Must file even if no tax is owed |
| Claiming certain reliefs | Higher-rate pension relief not via PAYE, Gift Aid (if above basic rate) |
Who Does NOT Need to File?
You generally do not need to file if you are:
- An employee or pensioner with income taxed entirely via PAYE, earning under £100,000
- Receiving only state pension income below the Personal Allowance
- Receiving dividends of £500 or less (within the dividend allowance)
- Receiving savings interest within your Personal Savings Allowance
- Trading income below £1,000 (covered by the Trading Allowance)
- Property income below £1,000 (covered by the Property Income Allowance)
If you are unsure, use the HMRC "Check if you need to send a Self Assessment tax return" tool at gov.uk — it takes about 2 minutes and gives a definitive answer.
How to Register for Self Assessment
If you have never filed a Self Assessment return before, you must register with HMRC by 5 October 2026 for the 2025/26 tax year. Late registration itself incurs a penalty (HMRC may charge a tax-geared penalty for any tax that was not paid on time due to late registration).
Registration steps:
- Go to gov.uk and search "register for Self Assessment"
- Choose your registration type: self-employed, not self-employed, or partner
- Complete the online form — you will need National Insurance number and personal details
- HMRC will post your Unique Taxpayer Reference (UTR) within approximately 10 working days
- Create a Government Gateway account and enrol for Self Assessment online services
- Once enrolled, you can file and pay online at any time before the 31 January 2027 deadline
Making Tax Digital ITSA: New from April 2026
Making Tax Digital for Income Tax Self Assessment (MTD ITSA) replaces the traditional annual return process with mandatory digital record-keeping and quarterly submissions for those with income above the thresholds:
- From April 2026: self-employed individuals and landlords with total income above £50,000 must comply
- From April 2027: threshold drops to £30,000
Under MTD ITSA, you will:
- Keep digital records using approved software (or HMRC's free tool)
- Submit quarterly summaries of income and expenses (by 7 August, 7 November, 7 February and 7 May each year)
- Make a final year-end declaration (replacing the current SA return, due by 31 January)
The 2025/26 Self Assessment return (due January 2027) is under the old system for most people — MTD ITSA quarterly submissions begin from 6 April 2026 onwards.
Late Filing and Payment Penalties
The penalty structure for the 2025/26 return if filed or paid late:
| Trigger | Penalty |
|---|---|
| 1 day late (1 February 2027) | £100 fixed penalty |
| 3 months late (1 May 2027) | £10/day for each day up to 90 days (max £900) |
| 6 months late (1 August 2027) | 5% of tax due or £300, whichever is higher |
| 12 months late (1 February 2028) | Further 5% of tax due or £300 |
| Interest on unpaid tax | 7.5% per annum from 1 February 2027 |
| Late payment: 30 days+ | 5% of unpaid tax |
| Late payment: 6 months+ | Further 5% of unpaid tax |
| Late payment: 12 months+ | Further 5% of unpaid tax |
Important: the £100 day-one penalty applies even if there is no tax to pay. If you have a reasonable excuse (serious illness, bereavement, system failure) you can appeal penalties via the HMRC appeals process.
If you genuinely cannot pay, contact HMRC before the deadline to arrange a Time to Pay agreement — spreading payments over 12 months or more. Interest still accrues, but penalties for non-payment may be reduced.