Do You Need to Register for UK Self Assessment by 5 October?

If you earned money outside of PAYE during 2024/25, whether from freelancing, renting out a property, or selling investments, there's a date you need to know: 5 October 2025. That's the deadline to register for Self Assessment if it's your first time filing.

Miss it and you risk penalties before you've even started filling in the return. Here's who needs to register, how to do it, and what happens if you're late.

Do you need to register?

Not everyone does. Here are the triggers:

Self-employed (sole trader): If your trading income was over £1,000 in 2024/25, you need to register. That's £1,000 gross, before expenses.

Partnership: All partners must register individually.

Untaxed income: Rental income, freelance earnings, side-job money, tips, commissions, savings interest, or dividends that weren't fully taxed through PAYE. If you had any of these, you likely need to register.

High Income Child Benefit Charge (HICBC): If your adjusted net income was between £60,000 and £80,000 in 2024/25 and you or your partner claimed Child Benefit, HICBC applies. Until July 2025, you generally had to file a Self Assessment return to pay it. From August 2025, HMRC is rolling out a new PAYE service that collects HICBC automatically for many employees, which means fewer people will need to file just for this. Check the latest HICBC guidance to see where you stand.

Capital gains: If you made disposals that trigger Capital Gains Tax (selling shares, a second property, etc.), you need to register.

Foreign income: Overseas property, interest, or dividends? Register.

PAYE-only income with no other triggers: You probably don't need to register. From 2024/25, having a high PAYE salary alone no longer automatically means you have to file. But you still need to if another trigger applies (CGT, substantial untaxed income, complex reliefs, HICBC not collectible through PAYE).

The £1,000 trading allowance: If your trading or miscellaneous income was £1,000 or less and you have no other reason to file, you're generally covered by the trading allowance and don't need to register. But if you want to claim actual expenses or report a trading loss instead of using the allowance, you must register and file.

Useful tools:

Key deadlines for 2024/25

The tax year ran from 6 April 2024 to 5 April 2025. Here's what comes next:

Deadline	What
5 October 2025	Register for Self Assessment (first-time filers)
31 October 2025	Paper return deadline
31 January 2026	Online return deadline and payment deadline

If you register after 5 October, HMRC will usually give you about three months to file once they confirm your obligation. But late registration can also attract a separate "failure to notify" penalty if you owe tax. That's on top of any late filing or late payment penalties. Just register on time.

See: Deadlines for Self Assessment (GOV.UK)

How to register: step by step

1. Gather your details. You'll need your National Insurance number, personal details (name, address, date of birth), and, if you're self-employed, your business start date and the type of work you do.

2. Pick the right registration route.

Self-employed/sole trader: Register for self-employment
Not self-employed but need to file (rental income, CGT, HICBC outside payroll): Register for Self Assessment

3. Wait for your UTR. HMRC will post your Unique Taxpayer Reference. It usually takes about 15 working days in the UK, longer if you're overseas. Keep it safe. You'll need it to file.

4. Set up your HMRC online account. Create or sign into your Government Gateway account and add the Self Assessment service.

5. File and pay by the deadlines. Submit your return online (or on paper by 31 October) and pay what you owe by 31 January. If the bill is going to be difficult to pay in one go, look into HMRC's Budget Payment Plan, which lets you spread payments across the year.

Penalties for getting it wrong

Late filing (missing the 31 January online deadline)

The penalties stack up:

Immediately: £100 fixed penalty (even if you owe no tax)
After 3 months: £10/day up to a maximum of £900
After 6 months: the greater of £300 or 5% of the tax due
After 12 months: another charge of £300 or 5% of tax due (higher penalties for deliberate non-compliance)

See: Penalties for late tax returns (GOV.UK)

Late payment (not paid by 31 January)

5% surcharge on unpaid tax at 30 days, 6 months, and 12 months
Interest runs from 1 February until you pay (HMRC sets the rate and it changes periodically)

See: If you do not pay your tax bill on time (GOV.UK) and HMRC interest rates

Failure to notify

If you don't tell HMRC you need to file and you owe tax, there's a separate penalty on top of everything else. The amount depends on how much tax was due and how long you waited. Register by 5 October to avoid this entirely.

Common situations

Capital Gains Tax

If you sold shares or a second property at a profit, you may need to file. For UK residential property, you also have to report and pay CGT within 60 days of completion through the UK Property Reporting Service, on top of including it in your Self Assessment return.

Even if your gains fall within the annual exemption, large disposal proceeds can create reporting requirements. Check HMRC's guidance: Report and pay Capital Gains Tax (GOV.UK)

Side hustles and platform income

If your total trading or miscellaneous income was £1,000 or less, the trading allowance usually means you don't need to file. Go above £1,000, and you need to register. If you want to claim actual expenses instead of the flat £1,000 allowance (useful if your costs were higher), you have to register and file even if income was under £1,000.

Worked examples

Zara, freelance designer with a PAYE job. Earned £42,000 through her employer and £5,000 from freelance design work in 2024/25. The freelance income is over £1,000 and wasn't taxed at source. She must register by 5 October 2025, get her UTR, and file her return by 31 January 2026.

Ben, occasional tutor. Earned £800 from tutoring in 2024/25. No other untaxed income. The £1,000 trading allowance covers this, so he doesn't need to register. If his expenses exceeded £800 and he wanted to claim them instead, he would need to register and file.

Don't leave it until October

The earlier you register, the sooner you get your UTR, and the more time you have to file without rushing. If you earned anything outside PAYE in 2024/25, run through the checks above and register now if you need to. The admin takes 10 minutes. The penalties for ignoring it are much worse.