Making Tax Digital for Income Tax (MTD ITSA): The Complete 2026 Guide

Making Tax Digital for Income Tax (MTD ITSA) is the biggest change to Self Assessment in a generation. From April 2026 the affected clients stop filing one annual return and start filing quarterly digital updates plus a final declaration. For accountants the work doesn't get bigger so much as it changes shape — four deadlines a year per client instead of one. This guide explains who is in, when, the deadlines, and how to prepare a book of clients.

Who has to comply, and when

MTD ITSA applies to self-employed individuals and landlords based on their qualifying income — broadly gross income from self-employment and property before expenses. It is being phased in by threshold:

Qualifying income is tested against the income reported on the most recent return HMRC has on file. A client whose 2024/25 return shows combined self-employment and property income above £50,000 is mandated from 6 April 2026. Partnerships are not yet in scope, and some groups (for example, those without a National Insurance number) are exempt.

The quarterly update deadlines

Once mandated, a client sends a cumulative quarterly update of income and expenses through MTD-compatible software. The standard quarters and deadlines are:

The updates are cumulative: each one restates the year to date, so an error in Q1 is simply corrected in Q2 rather than requiring an amendment. The first mandated update — Q1 of 2026/27 — is due 7 August 2026. Full deadline details are on the MTD ITSA quarterly update deadline page.

Standard vs calendar quarters

Clients (or their software) can elect to use calendar quarters ending 30 June, 30 September, 31 December and 31 March instead of the standard 5th-of-the-month periods. The deadlines are the same (7 August, 7 November, 7 February, 7 May), so the election is purely about which day the period ends — calendar quarters line up neatly with bookkeeping done to month-end. The election should be made before the first update of the tax year.

The final declaration

After the four quarterly updates, a final declaration finalises the year — adding any non-business income, claiming reliefs and allowances, and confirming the figures. It is due by 31 January following the tax year, the same date the Self Assessment return used to fall, and it replaces the SA return for mandated clients. The 31 January and 31 July payment dates for tax and payments on account are unchanged. See the MTD ITSA final declaration deadline page for the full schedule.

Penalties

MTD ITSA uses the points-based late-submission penalty model: each late quarterly update earns a point, and reaching the threshold (four points for quarterly filers) triggers a £200 penalty, with further £200 penalties for subsequent failures. Late-payment penalties and interest follow the same regime as the rest of Self Assessment. For the first year of mandation (2026 to 2027), HMRC has confirmed there are no penalties for missing a quarterly update deadline — though late-payment penalties and interest still apply, and the safest plan is to file every update on time from the start.

Preparing a book of clients

The practical work is front-loaded: identify who crosses the threshold, confirm each client has compatible software, get them keeping digital records from 6 April, and set the quarterly rhythm. The risk for a practice is volume — a single 7 August or 7 November deadline now applies to dozens of clients at once, where before the work was spread across the January season. Tracking which clients are mandated and which quarter election they're on, and flagging each deadline in advance, keeps the new cadence manageable.

Guides in this series

This guide is the hub for our detailed MTD for Income Tax articles:

Detailed guides in this series are publishing through 2026 — check back soon, or use the deadline checker below in the meantime.

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This is general information, not advice — check the current GOV.UK guidance, or a client's specific position with a qualified accountant, before acting.
Sources
GOV.UK — Making Tax Digital for Income Tax: https://www.gov.uk/guidance/use-making-tax-digital-for-income-tax
GOV.UK — Check when to sign up for Making Tax Digital for Income Tax: https://www.gov.uk/guidance/check-when-to-sign-up-for-making-tax-digital-for-income-tax
GOV.UK — Penalties for Making Tax Digital for Income Tax: https://www.gov.uk/guidance/penalties-for-making-tax-digital-for-income-tax