SA1: register for Self Assessment if you're not self-employed

Who needs it

• People who need to send a tax return for a reason other than self-employment, such as owing Capital Gains Tax, receiving trust income, or having untaxed income from property or a pension.
• Anyone in that position who has never sent a tax return before.
• People who can't register online, including anyone who doesn't live in the UK: HMRC's online service isn't open to them.
• Not sole traders: they register as self-employed online or on form CWF1. Partners use form SA401.

What you need before you start

• Your personal details.
• The reason you need to complete a tax return, for example a gain you need to pay Capital Gains Tax on or income from a trust.
• Government Gateway or GOV.UK One Login sign-in details if you register online. You can create them when you first sign in.
• Photo ID such as a passport or driving licence, in case the online service asks you to prove your identity.

How to file SA1

1. 1Check that you need to send a tax return. HMRC's checker on GOV.UK gives a definite answer.
2. 2Register online through HMRC's registration service if you can. You can save your progress and come back later.
3. 3If you can't register online, fill in form SA1 on screen, print it and post it to the address shown on the form.
4. 4Wait for your Unique Taxpayer Reference (UTR): within 72 hours in your personal tax account if you registered online, or usually 15 working days by post (21 if you're abroad).
5. 5File your return and pay any tax due by the deadlines. If you registered by 5 October, the online return and payment are both due by 31 January.

Online first, SA1 if you can't

HMRC's preferred route is its online registration service. You sign in with Government Gateway or GOV.UK One Login, may be asked to prove your identity with photo ID, and your UTR appears in your personal tax account within 72 hours. HMRC launched an improved version of the service for individuals with a personal tax account in September 2026.

Form SA1 is the fallback. HMRC's guidance is to fill it in on screen, print it and post it to the address on the form. You'll need your personal details and the reason you need a return. It's also the route for anyone who doesn't live in the UK, because the online service isn't open to them.

SA1, CWF1 or SA401

HMRC has a different registration route for each situation. SA1 is for people who aren't self-employed. Sole traders register as self-employed, online or on form CWF1, which also registers them for Class 2 National Insurance. Partners in a business partnership use form SA401, and the nominated partner registers the partnership itself as well.

Agents aren't covered by the new online service. HMRC says agents should keep using the existing processes, including CWF1 or SA1, to register a client.

The 5 October deadline

You must tell HMRC by 5 October if you need to complete a tax return for the previous tax year and either haven't sent one before or didn't need to send one the year before. Register on time and the online return is due by 31 January.

Register after 5 October and HMRC sends a letter or email setting a filing deadline three months from its date, but the tax is still due by 31 January, and you could get a penalty for telling HMRC late.

Common mistakes

• Using SA1 when you're self-employed. Sole traders register as self-employed, online or on CWF1, which also covers Class 2 National Insurance.
• Registering again when you've registered before. If you didn't need to send a return last year, HMRC asks you to reactivate your existing account instead.
• Registering after 5 October. HMRC can charge a penalty, and although it sets a later filing deadline, the 31 January payment date doesn't move.
• Assuming the UTR will arrive in time on paper. A postal registration takes longer, so leave room before the filing deadline.