How to sign up a client for MTD for Income Tax as an agent: authorisation, the 21-day link and clients HMRC has signed up itself

An agent can sign a client up for Making Tax Digital for Income Tax, but only from an agent services account, only once the client's authorisation is in that account, and only one client at a time. GOV.UK spreads the detail over several pages. This guide puts it in the order a practice meets it.

Who can be signed up

GOV.UK sets two conditions: the client is registered for Self Assessment and has submitted a tax return in the last 2 years. A client with qualifying income over £50,000 has had to use the service since 6 April 2026. Qualifying income is self-employment and property income before expenses, and for 2026 to 2027 HMRC takes it from the 2024 to 2025 return. A client below the threshold can volunteer for the current tax year or the next. Our MTD deadline checker works out the start date for each client.

Once per practice: the account and the authorisations

The agent services account. It is a different account from HMRC online services for agents. The application asks for the name of the practice's anti-money-laundering supervisory body and proof of supervision. HMRC says it will reject an application where supervision has been applied for but not yet approved. A practice that still needs supervision should read our guide to HMRC AML supervision fees and registration first.

Existing Self Assessment clients. HMRC recognises existing Self Assessment authorisations for MTD, but they have to be added to the agent services account. Sign in, choose "Add existing Self Assessment authorisations to your agent services account" and enter the Self Assessment agent code. The screen then lists agent codes, not clients. A practice with more than one agent code repeats the step for each. Adding a code does not sign any client up.

Clients with no authorisation yet. Create an authorisation request in the agent services account. The agent sends the client a link by email, and the client signs in with their own details to accept it. The link expires after 21 days. An agent must never sign in with a client's credentials.

What to collect for each client

The steps, client by client

1. Check whether the client is exempt. An exempt client does not sign up.
2. Confirm the authorisation is in the agent services account, by agent code or by a completed request.
3. Collect the details in the table above.
4. Sign in with the agent services account user ID and sign the client up. Check each income source the service shows and add any that are missing.
5. Authorise the client's compatible software and check the accounting period in it.
6. Use the software to send any quarterly updates already missed for the year.
7. File the 2025 to 2026 Self Assessment return as usual. Its deadline is still 31 January 2027, under the old penalty rules.

The 21-day link, worked through

A request sent on Monday 5 October 2026 expires 21 days later, on Monday 26 October. Chase on day 7 (12 October) and day 14 (19 October). If the link lapses, the agent has to send a new one. The next quarterly update is due on 7 November 2026, which is 12 days after 26 October. A request sent after 17 October does not expire until after that deadline, so an ignored link can run straight past it.

If HMRC has already signed the client up

GOV.UK says that from September 2026 HMRC signs up, in stages, anyone who needs to use the service for 2026 to 2027 and has not signed up. The client gets a letter in their HMRC online account or by post. HMRC uses only what it holds: the 2024 to 2025 return, plus the 2025 to 2026 return if that was filed first.

For these clients an agent checks three things in the agent services account: the authorisation has been added, the client's Unique Taxpayer Reference appears, and MTD for Income Tax has been added. Then search for the client by UTR and check the income sources HMRC has recorded.

Two cases need action quickly:

• All income ceased before 6 April 2026. Update the client's information. The client does not use the service but still files the 2025 to 2026 return.
• All income ceased on or after 6 April 2026. The client still sends a quarterly update up to the date of cessation and files the 2026 to 2027 return through the service.

An agent who disagrees that a client belongs in the service is told to contact the agent dedicated line.

Penalties in the first year

HMRC will not apply penalty points for late quarterly updates in 2026 to 2027. Penalties still apply for a late tax return and for late payment. For later tax years each missed deadline earns one point, and at 4 points the client pays £200, then £200 for each further missed deadline. The updates still have to be sent this year, because the final quarterly update must be in before the return can be submitted.

Four blocks and their causes

Once the client is in, the work becomes the quarterly routine in what a practice does each quarter, and the chasing starts with the records request letters.

Overlyft can set up an AI assistant to collect the sign-up details and chase an unanswered authorisation link. Tax advice and sign-off stay with the accountant.

This is general information, not professional advice.