If you're newly self-employed, becoming a landlord, or otherwise earning income HMRC doesn't already know about through PAYE, you'll usually need to register for Self Assessment. Missing the deadlines can mean automatic penalties even if you don't actually owe any tax, so it's worth understanding the process before your first year of trading is over.
Who needs to register
You generally need to register for Self Assessment if, in a tax year, you:
- Are newly self-employed or a sole trader with income above the trading allowance threshold.
- Earn income from renting out property above the level covered by existing allowances.
- Have significant untaxed income, such as investment income, dividends above your dividend allowance, or foreign income.
- Need to claim certain reliefs or repayments that require a return, or your income (or your partner's) triggers the High Income Child Benefit Charge.
- Are a partner in a business partnership.
If your only income is taxed through PAYE and you have no other significant income, you typically won't need to register — but if in doubt, HMRC's online checker tool will confirm whether you need to.
Key deadlines
| Milestone | Deadline |
|---|---|
| Register for Self Assessment | By 5 October following the end of the tax year in which you started |
| File your online tax return | By 31 January following the end of the tax year |
| Pay any tax owed | By 31 January following the end of the tax year (with a possible second "payment on account" by 31 July) |
For example, if you started self-employment at any point between 6 April and the following 5 April (the tax year), you must register by 5 October after that tax year ends, and file and pay by the following 31 January.
Step-by-step: how to register
- Step 1: Determine your registration type. Registering as newly self-employed, as a landlord, or for other untaxed income each uses a slightly different route through GOV.UK.
- Step 2: Create or use your Government Gateway account. You'll need a Government Gateway user ID and password to register and later file online — set this up in advance if you don't already have one.
- Step 3: Complete the registration form on GOV.UK. This asks for personal details, National Insurance number, and information about the income or activity triggering registration.
- Step 4: Receive your Unique Taxpayer Reference (UTR). HMRC posts this 10-digit number, usually within about 10 working days (longer if you're outside the UK) — you'll need it for every future return.
- Step 5: Activate online filing. HMRC sends a separate activation code to set up your online Self Assessment account, needed before you can file your first return.
What happens if you register late
Registering after the 5 October deadline doesn't automatically trigger a fixed penalty by itself, but it puts you at serious risk of missing the 31 January filing deadline, which does carry automatic penalties — starting with a fixed late-filing penalty even if you owe no tax, with further daily and percentage-based penalties the longer it remains outstanding, plus separate penalties and interest for paying tax late. Registering as soon as possible after you're required to reduces this risk considerably, since HMRC needs time to issue your UTR and activation code before you can even file.
Common mistakes
- Waiting until January to register — the UTR and activation code can take weeks to arrive, potentially leaving too little time to file before the 31 January deadline.
- Assuming no tax owed means no need to register or file — registration and filing obligations exist independently of whether tax is actually due.
- Not budgeting for "payments on account" — from your second year, HMRC may ask for advance payments towards next year's tax bill alongside the current year's, which can come as a shock if unplanned.
What to do next
If you've started self-employment, letting income, or other untaxed income this tax year, register with HMRC well before the 5 October deadline rather than waiting — set a reminder as soon as your activity starts, and keep records of income and expenses from day one so your first return is straightforward to complete.