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

Introduction

Side jobs, freelance gigs, or rentals: have you had any? If it's your first tax return, you must register for Self Assessment by 5 October after the tax year ends; if not, it will cause delays in accessing HMRC systems and potential penalties.

Provided below are quick "yes/no" checks, the registration steps, the key deadlines of 2024/25, what happens if you get late—plus links to the official GOV. UK.

Who must register? Quick decision guide

Not everyone has to pay a return. These are UK-specific triggers:

Self-employed (sole trader): total trading income exceeding £1,000 before expenses for 2024/25 → Register.
Business partnership: partners must register.
Untaxed incomes: for example, rental incomes, freelancing, side jobs, tips, commissions, certain incomes from savings and dividends not fully taxed → Register.
High Income Child Benefit Charge (HICBC):
Until July 2025: you must register if HMRC cannot collect this via PAYE.
From August 2025 onward: new PAYE service will roll out to collect HICBC for a large number of employees; therefore, registration will be required only in those instances where HMRC is unable to collect it in this manner. Always check the latest guidance.
Capital gains: if CGT is payable or disposals arise reporting obligations → Register.
Foreign income: e.g., overseas property, interest, dividends → Register.

-PAYE-only income (employment/pension) with no other triggers: generally, you will not need to register for Self Assessment for 2024/25 onward.

Some PAYE-only taxpayers still have the obligation to do so. For example, when claiming certain reliefs and if you have complex expenses or if HICBC cannot be collected via PAYE.

Trading allowance tip: You generally must not register if your trading/misc income is £1,000 or less and you have no other reason to file. Conversely, if you want to claim actual expenses or a trading loss instead of the £1,000 allowance, you must register and file.

Helpful tools:

Key UK deadlines for the 2024/25 tax year

Tax year: 6 April 2024 - 5 April 2025

5 October 2025 → Deadline to register if this is your very first time.
31 October 2025 → Deadline for the paper return.
31 January 2026 → Deadline for online returns, as well as for payments.

Late registration? Usually, HMRC will specify a filing deadline of about three months when it confirms you have to file.

Registering up after 5 October might also attract a failure to notify penalty if you owe tax: This penalty is separate from penalties for late filing and late payment, so just make sure you get registered on time.

See: Deadlines for Self Assessment

How to register for Self Assessment (step-by-step)

Step 1: Gather your details

National Insurance number
Personal details (name, address, date of birth)
Business info for self-employed status (start date, type of work)

2) Select an appropriate route

Sole traders/self-employed: Register for self-employment and Register for Class 2 NIC
Not self-employed but need to file (e.g. rental income, CGT, HICBC outside payroll):Register for Self Assessment (not self-employed)

3) Wait for your UTR

HMRC mails your Unique Taxpayer Reference (UTR)—generally around 15 days in the U. K., somewhat longer if overseas. Keep it safely.

4) Set up the Gateway

Create/sign in to your HMRC online account and add the Self Assessment service.

5) Respect deadlines for filing and payment

File online or print and send paper form (or via approved software) and pay by 31 January. Or consider a Budget Payment Plan, if that might be useful.

Penalties and interest for late submissions

Late filing (missing 31 January online deadline)

A fixed penalty ofin £100 irrespective of any tax being due.
After 3 months: £10 per day (up to £900).
At 6 months: the greater of £300 or 5% of the tax due.
At 12 months: the greater of £300 or 5% of the tax due (higher penalties may apply for deliberate behaviour).

See: Penalties for late tax returns

Late payment (not fully paid by 31 January)

5% of any unpaid tax at 30 days, 6 months and 12 months.
Interest runs from 1 February until payment (HMRC sets the rate and it can change).

See: If you do not pay your tax bill on time and Interest rates for late payments

Failure to notify (not telling HMRC you need to file)

Another penalty can be charged by HMRC where you fail to notify, this depending on the tax that was due and the time the non-notification was. Register by the deadline of 5 October to avoid this.

Special cases and FAQ

High Income Child Benefit Charge (HICBC)

From 6th April 2024, HICBC kicks in at £60,000 and is fully repaid at £80,000).
If HMRC can actually collect it through PAYE, you may not actually have to file Self Assessment. From August 2025, that would largely be taken care of automatically by a new PAYE-based service for many employees.
Make sure to use the calculator set out by HMRC and check your own adjusted net income before deciding.

See: Child Benefit tax charge (HICBC)

Capital Gains Tax (CGT)

Filing is required if you have CGT to pay: for example disposing of shares or a second property.
In the case of UK residential property gains where tax due-have to report and pay within 60 days of completion via UK Property Reporting Service.
Large disposal proceeds can create reporting requirements even with gains under the annual exemption—check HMRC guidance and SA notes.

See: Report and pay Capital Gains Tax

Side hustles, platforms, and small sales

If trading/miscellaneous income totals up to £1,000, usually the trading allowance covers it and no return filing is necessary.
If one wants to claim actual expenses (or made a loss), then registration and filing will need to be done instead of claiming the allowance.

PAYE-only high earners

For years from 2024/25 onward, high PAYE earnings alone will no longer automatically trigger filing of self-assessment.
You still have to file if another trigger applies (e.g., CGT, substantial untaxed income, complex reliefs, HICBC not paid through PAYE).

Worked examples

Example 1 — Freelance designer with PAYE job

Zara earned £42,000 via PAYE and £5,000 from freelance design in 2024/25.
Outcome: She must register by 5 October 2025, get a UTR, and file by 31 January 2026. Usual late filing/payment penalties apply if she misses deadlines.

Example 2 — Occasional tutoring under the trading allowance

Ben earned £800 in tutoring in 2024/25, with no other untaxed income.
Outcome: He doesn't have to register or file (assuming there are no triggers to do so). If he wishes to deduct actual expenses greater than £800, he needs to register and file.

Conclusion

If revenue given out of PAYE in 2024/25 form self-employment, renting, investment, or gains, register by 5 October 2025. The earlier the registration, the more time to get your UTR, file online, and avoid fines. Go forward with the checks above plus the steps, and visit GOV. UK if need. Admin now saves a lot of stress later.