Quick answer
One year is enough. HMRC decides from the qualifying income on your tax return, so a single year over the threshold means you need MTD from the start of the following tax year. You can only opt out after three tax years in a row below the threshold.
Key facts
One return over the threshold triggers MTD
HMRC writes before the year you need to start
Opting out needs 3 years in a row below the threshold
Exemptions still apply if you qualify
Example
A sole trader whose turnover is usually £24,000 has an unusual year with £34,000 on their 2025/26 return. They need MTD from 6 April 2027. If their income then drops back, they stay in until they’ve been below the threshold for three tax years in a row.
Is it worth fighting?
Usually not. Once your records are in software, quarterly updates take little time. If you genuinely can’t use digital tools, you can apply for an exemption instead.
Thresholds are falling
The threshold drops to £30,000 from April 2027 and £20,000 from April 2028, so many people near the line will be in MTD before long anyway.