HMRC agent authorisation for Self Assessment: how long it takes, and the last safe date before 31 January

Free checker: when will you have access, and how late can you start?

Code or 64-8: which route for which tax

From gov.uk's How to get authorised to act as a tax agent (updated 7 October 2026), for the taxes most bookkeepers meet:

Start with the code for Self Assessment. HMRC publishes a time for the letter, and you can see when it's done. Use the 64-8 when a posted code isn't practical, for example a client who's abroad or very slow with post, when you need individual PAYE too, or as a second attempt. Nothing we read on gov.uk stops you trying both, but a new authority replaces any existing one, so an existing agent loses out either way.

To use any of this you need an agent code and the Self Assessment for Agents service on your HMRC online services account. If you don't have them yet, start with gov.uk's steps before registering as a tax agent, and do it well before January.

The code, step by step

1. Sign in to your HMRC online services for agents account. This is a different sign-in from your agent services account.
2. Select "Authorise client", then "Request an authorisation".
3. Pick the tax service and enter your client's details. The service tells you what it needs.
4. Message your client the same day. The letter goes to them, not you, and it's easy to bin (the checker above writes the message).
5. When they tell you the code, go back to "Authorise client", select "Enter authorisation code", pick the client and enter it.
6. The client then appears on your client list.

• One code per tax. If you ask for Self Assessment and Corporation Tax, your client gets two codes. Make sure you know which is which.
• Three wrong entries and you start again, so ask for a photo of the letter rather than a code read out over the phone.
• Busy periods: gov.uk warns online services may be slow, and has a page for service issues.

Source: How to use the Online Agent Authorisation.

Filling in a 64-8 so it doesn't bounce

Get form 64-8 from gov.uk (the version we read was updated June 2025). gov.uk's instructions are stricter than you might expect:

• Type it or write clearly, and write nothing outside the boxes.
• Agent code (SA): only the code, 6 characters in the format 1111XX. Don't add anything else in the field.
• Don't strike through unused boxes.
• No covering letter unless it has essential information needed to process the form.
• Self Assessment box: if ticked, give the client's National Insurance number and/or UTR. There's a box to tick if the UTR hasn't been issued yet.
• Statement of Account: by default it goes to your client. There's a box to tick if it should come to you. Your client stays responsible for paying.
• Send pages 1 and 2 only, and keep page 3. The form's address (check it on the form itself in case it has changed) is National Insurance Contributions and Employer Office, HM Revenue and Customs, BX9 1AN.
• Who signs: the individual for personal tax, and for a partnership, the partner responsible for its tax affairs. Each partner signs a separate authority for their own tax.

When the code doesn't come

In order:

1. Count the days. HMRC's 7 working days plus post. If you requested it on 21 December, the letter may not go out until 4 January, because of the bank holidays.
2. Ask about the address. gov.uk says it's posted "to your client". We'd expect it to use the address HMRC holds, so a client who moved without telling HMRC is the first thing to check. Your client can update it themselves, then you request a new code.
3. Ask them to look again. It's a plain HMRC letter, so it may be in the pile, or they may have put it aside without knowing what it was.
4. Check whether it has lapsed. After about 30 days from issue you have to start again anyway.
5. Request a new code, and consider a 64-8 as well if there's time for it. Make a note of the date you did each, in case a penalty is disputed later.

No UTR yet? gov.uk says the client must register for Self Assessment before authorising an agent. A 2011 ACCA note (old, and we only read a summary of it) said a 64-8 sent before registration might not link to the client's record. Send them to our sister site's page on waiting for a UTR. Registered agents can also use the helplines on gov.uk's dedicated contacts for tax agents page.

When it's too late for 31 January

Being unauthorised doesn't stop the deadline, or the bill. Client responsibility is clear on gov.uk: "You'll still be legally responsible for your own tax." So:

• The client can file it themselves from their own HMRC account, using figures you've prepared. They sign in and they submit. You can't do it for them with their login: gov.uk says an agent must not use a client's credentials to sign in to any account. Check this early, because a client who has never filed online may need time to set up, and HMRC's online service can't take every return (partnerships and non-residents, for example). Paper returns were due by 31 October.
• They can pay without you. The 5% late payment penalties and the interest run on the bill, whoever is handling the return. See what to do if they can't pay by 31 January.
• The £100 late filing penalty applies even if there's no tax to pay. Don't tell a client that waiting for HMRC's letter will be accepted as a reasonable excuse: we haven't found anything from HMRC that says so. See how the penalties add up.
• Keep the authorisation going, so you can deal with statements and questions afterwards.

What about filing through your software before you're authorised? We couldn't confirm this from gov.uk. A 2009 note from IRIS said registered agents didn't need a 64-8 in place to file through its software, though they did with HMRC's software, and did to discuss a client's position. Search summaries of accountants' forum threads say something similar (we couldn't open the threads themselves). That's old and thin, so ask your software supplier, and don't plan a client's filing around it. You'd also still need the client's approval of the return, and gov.uk says they must check it and tell you it's correct before you submit.

Making Tax Digital clients

Self Assessment authorisation sits on your HMRC online services account. Making Tax Digital for Income Tax sits on your agent services account. To link them, sign in to your agent services account and select "Add existing Self Assessment authorisations to your agent services account". You enter the Self Assessment agent code, and it adds all the authorisations under that code as main agent. It doesn't sign any client up for Making Tax Digital.

The other route is the digital handshake: you send your client a link, and they have 21 days to respond. If your client doesn't respond in time, you start again. Once the agent code is linked, gov.uk says clients you add or update for Self Assessment in your online services account update your agent services account permissions too.

One trap: a digital handshake for the Income Record Viewer only lets you see income data. gov.uk says you still need a 64-8 or Online Agent Authorisation to speak to HMRC for that client.

Sources: Add your client authorisations for MTD, How to use the digital handshake. See also our Making Tax Digital guide.

Build it into every new client

Authorisation is step 5 of our client onboarding checklist, but ask for it on day one, straight after your money laundering checks. Set a rule for the season: any client taken on after your last safe date gets told in writing, before you accept the work, that filing on time may depend on them filing it themselves. Our engagement letter template and records chasing schedule cover the rest of that conversation.

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