The MTD Notebook · For agents · 8 August 2026

MTD for accountants and bookkeepers: signing up, authorising and filing for clients

Making Tax Digital for Income Tax does not change the tax. It changes the rhythm of the work, and it changes it per client — a new account to hold your authorisations, a sign-up you must do for each client individually, and four cumulative updates a year instead of one return. This is what actually changes for a practice, in the order you hit it, with every step checked against GOV.UK and dated.

1. What actually changes for a practice

The liability calculation is unchanged. Payments on account are unchanged. What changes is that each mandated client moves from one Self Assessment return a year to four quarterly updates plus a final declaration — and the updates are cumulative, so they restate the year to date rather than reporting a single quarter. The final declaration replaces the Self Assessment return.

Two consequences fall straight onto the practice, not the client:

• The work is per client, four times a year, on fixed dates. The quarterly deadlines — 7 August, 7 November, 7 February, 7 May — are the same for everybody and do not move with a client's accounting date. Your whole mandated book lands on the same four dates.
• Sign-up is not automatic and not bulk. As you will see below, HMRC requires you to sign up each client individually, even where the authorisation already exists.

2. The account you need — and the one that no longer does the job

To act for clients under MTD you need an agent services account (ASA). GOV.UK is explicit that this is not the same thing as your existing HMRC online services for agents account — it is a separate account, and a practice has one ASA. If you have already been using an ASA for VAT MTD, it is the same account; you do not need a new one.

Everything for MTD for Income Tax — adding authorisations, signing clients up, and filing — runs through the ASA using the user ID and password you got when you registered it.

3. Authorising a client (your Self Assessment authorisation mostly carries over)

This is the part that saves the most time, and the part most likely to be got wrong. GOV.UK states that existing client authorisations for Self Assessment are recognised for Making Tax Digital for Income Tax. You do not have to re-paper a 64-8 for a client you already act for.

There is one thing to check and one trap to avoid:

• Check the authorisation is actually in your ASA. If you are already authorised for Self Assessment, the authorisation may need adding into your agent services account. GOV.UK publishes a step for checking and adding your client authorisations for MTD.
• Adding the authorisation does not sign the client up. HMRC states plainly: "Adding authorisations will not automatically sign up your client for Making Tax Digital for Income Tax — you still need to sign up each of your clients individually through the online service." Treating the authorisation and the sign-up as one step is the mistake that leaves a client unregistered.

If you are not already authorised for a client, you sign into your ASA and follow the steps to ask the client to authorise you — the digital handshake. Where you are already authorised for MTD through a digital handshake, you can sign the client up without manually adding the authorisation first.

4. Signing a client up — what you need to hand

You sign each client up through HMRC's online service. Before you can, GOV.UK requires the client to be registered for Self Assessment and to have submitted a tax return in the last two years — the same return that determines whether they are mandated, and from when. You (or the client) still have to file the Self Assessment return for the year before they start using MTD.

To sign a client up you will need their:

• full name, date of birth and National Insurance number;
• for a sole trader — business name (as used on invoices), business address and the nature of the trade;
• for each income source — the business or property start date if it falls within the last two tax years, and confirmation of the tax year they will start using MTD.

If a client has multiple self-employments or property businesses, HMRC requires you to check each source in the service and add any that are missing. And if all of a client's self-employment or property income has ceased, you need to tell HMRC before the start of the next tax year — otherwise they will still be brought into MTD.

A client can also sign up voluntarily ahead of their mandation date — useful for getting a practice's processes bedded in on a willing client before the wave arrives. If they sign up mid-year, you will need software to send any quarterly updates already missed for the year so far.

5. What you file each quarter, per client

Each quarterly update covers from the start of the tax year to the end of the update period — not just the previous three months. Updates are cumulative: the second update restates 6 April to 5 October, not July to October. Two rules make the per-client work lighter than the four-a-year rhythm suggests:

• Under £90,000 turnover for a source, the client reports consolidated totals — one income figure and one expenses figure, no category breakdown. A large share of the first wave qualifies, because the wave starts at £50,000.
• No adjustments in a quarterly update. No capital allowances, no private-use adjustments, no accruals — those happen once, at the final declaration.

Because each update restates the year, an error in one is superseded by the next; for the first three quarters there is no separate amendment to file. The liability, the allowances and the adjustments all land once a year at the final declaration, which for 2026–27 is due 31 January 2028 — the same date as the balancing payment.

6. The first-year soft landing, and what it does not cover

This is where a lot of client-facing advice is a year out of date. For clients mandated from 6 April 2026, GOV.UK confirms HMRC will not apply penalty points for late quarterly updates for the first year (2026 to 2027).

The points-based system for late updates begins in 2027/28: one point per missed update or return, and a £200 penalty once a client reaches four points, then £200 for each further miss. For clients who sign up voluntarily, the penalty position differs again — HMRC contacts them to confirm when they become liable — so it is worth reading the volunteer guidance before recommending an early sign-up.

7. Planning the practice workload across the three waves

The audience only grows, and it grows by statute rather than by anyone's marketing. Each wave's start date is fixed by a return the client has already filed, so you can build the list now:

The 2027 wave is already determined — it depends on the 2025–26 return, due by 31 January 2027. Any client whose combined self-employment and property turnover topped £30,000 on that return has a start date fixed now, which means the useful conversation with them happens this year, not next. The step-by-step for signing them up runs the same way: agent services account, check the authorisation, sign up each client individually, then file.

The MTD Notebook covers the mechanics your clients will ask about — the full deadline calendar for all three waves, and what the first quarterly update actually showed once 864,000 people had filed one.