You need to file a 2025/26 Self-Assessment return if, in the tax year 6 April 2025 to 5 April 2026, you fell into one of the situations HMRC lists as requiring a return[1]. If this is your first return, the deadline that bites first is registration: tell HMRC by 5 October 2026. The online filing deadline is 31 January 2027. Not sure? Work through the table below before you assume you are out of scope.
Who must file a 2025/26 return?
| Trigger | Threshold | Return needed? |
|---|---|---|
| Self-employed sole trader[1] | Income over £1,000 before tax relief | Yes |
| Business partner[1] | A partner at any point in the year | Yes |
| High Income Child Benefit Charge[4] | You or your partner over £60,000 and getting Child Benefit (in full at £80,000), not paid via your tax code | Yes |
| Capital Gains Tax[1] | Tax due on a gain, e.g. a second property or shares | Yes |
| Untaxed income[1] | Rent, tips, commission, savings, dividends, or foreign income PAYE did not tax | Yes |
When are the 2025/26 deadlines?
Registration comes first if you have never filed before, or did not need to file last year. The gov.uk deadlines page[2] sets them out:
| What | Deadline | Applies to |
|---|---|---|
| Register for Self-Assessment | 5 October 2026 | First-time filers, or anyone who did not need to file for 2024/25 |
| Paper tax return | 31 October 2026 | Anyone filing on paper rather than online |
| Online tax return | 31 January 2027 | Everyone filing online |
| Pay the tax you owe | 31 January 2027 | All filers, however you filed |
| First payment on account[6] | 31 January 2027 | Larger bills: a payment toward next year's tax, 50% of this year's |
| Second payment on account[6] | 31 July 2027 | The other 50%, unless your bill is small or mostly taxed at source |
What happens if you miss the 5 October registration deadline?
Missing 5 October does not stop you filing, but it can trigger a separate penalty. If you owe tax and do not tell HMRC you are chargeable by the deadline, you may face a failure-to-notify penalty[5], a percentage of the tax due, lower if you disclose before HMRC contacts you and higher if the failure was deliberate. The tax itself is still due by 31 January 2027, so register the moment you know you are in scope.
What if I no longer need to file?
Filing is not automatic to switch off. If your circumstances changed, for example you stopped being self-employed[7] or no longer have untaxed income, you must tell HMRC so it stops issuing a return. Until you do, HMRC still expects one, and a missed return HMRC expected can attract late-filing penalties even if no tax is due. A final return for the last year you traded is still required.
How do you file a 2025/26 return?
If you decide you need to file, the process runs in this order:
- 1
Register with HMRC
Use the register for Self Assessment[3] service. HMRC sends you a Unique Taxpayer Reference (UTR) by post, which can take up to about 10 working days, so leave time before 5 October 2026.
- 2
Set up your online account
Enrol for the Self Assessment online service with your Government Gateway sign-in. HMRC posts an activation code, adding another few days, so do not leave registration to the deadline.
- 3
Gather your figures
Collect your income records for the year: business income and expenses, rental income, dividend vouchers, and any P60 or P45 for employment income already taxed under PAYE.
- 4
File the return and pay
Complete the return online by 31 January 2027 and pay the tax you owe by the same date. If you file on paper instead, the return is due earlier, by 31 October 2026.
Primary sources
- 1.Who must send a tax return — gov.uk — The situations that require a Self Assessment return, including the £1,000 sole-trader threshold
- 2.Self Assessment tax return deadlines — gov.uk — Register by 5 October; paper by 31 October; online by 31 January
- 3.Register for Self Assessment — gov.uk — How to tell HMRC you need to file, by the 5 October deadline
- 4.High Income Child Benefit Charge — gov.uk — The charge applies to income over £60,000, and in full at £80,000
- 5.Penalties: failure to notify — HMRC (CH70000) internal manual — gov.uk — The penalty for not telling HMRC you are chargeable to tax on time
- 6.Understand your Self Assessment tax bill: payments on account — gov.uk — Two advance payments, due 31 January and 31 July, each half of the previous year's tax
- 7.Stop being self-employed — gov.uk — Tell HMRC when you stop trading so it stops expecting a return; a final return is still due
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