Test one taxpayer against the MTD line

£52,000 is the number that decides it, and a Bristol sole trader who lets one flat hits it without noticing: £38,000 of self-employment turnover plus £14,000 of gross rent on the 2024-25 return. That return is the test, and it puts them inside Making Tax Digital for Income Tax from 6 April 2026, with a first quarterly update due 7 August 2026 and three more after it.

Almost everyone who gets this wrong gets it wrong the same way: they test profit. After expenses the same trader is nowhere near £50,000 and concludes they are out. HMRC's qualifying income test does not look at profit. It adds up gross receipts — turnover before expenses, plus gross rents before the mortgage interest and the letting agent. Two income streams that each look small combine into a number that is over the line.

The second way it goes wrong is the year. The threshold is not tested against the year you are in. GOV.UK is explicit: the April 2026 start was checked against the 2024 to 2025 return, the April 2027 start (over £30,000) against 2025 to 2026, and the April 2028 start (over £20,000) against 2026 to 2027. The return that decides it was filed in January 2026, and you cannot change it now. Anyone still repeating the abandoned April 2024 start date — and chatbots trained on older material still do — is answering a question that stopped existing two reschedules ago.

The third is part-year trading. If the business ran only part of the tax year, the receipts are scaled up to twelve months for the test: six months at £26,000 is tested as £52,000. A business that started in October and looks half-size on paper can be mandated on a doubled figure it never actually earned.

Then the dates, which are the part people have to live with. Quarterly updates land on 7 August, 7 November, 7 February and 7 May, and the final declaration replaces the return — for a 2026-27 start, 31 January 2028. Four dates a year instead of one.

Missing the payment costs real money on a published schedule: 3% of the tax still unpaid at day 15, another 3% at day 30, then 10% a year charged daily on what is left. On an £8,000 balancing payment that is £240, then £480, then a daily charge on top, with interest separate. There is a first-year easement that adds fifteen days before the first penalty bites, which is why the same £8,000 paid forty days late costs £240 with the easement and £501.92 without it. That is a 109% difference produced by one checkbox, and it is exactly the kind of detail a general-purpose answer will not track.

So the free checker does the whole test and keeps nothing back. You put in the two gross figures, the return year, the months traded, the tax owed and the days late, and it returns eight answers: the annualised qualifying income, the verdict against that year's threshold, the 6 April you are mandated from, the first update date, all four quarterly dates, the final declaration date, the modelled penalty, and the working that produced it. No key, no client limit, no locked results, and the popup and the web page run the same code.

The paid layer is a different axis, not a crippled version of the same one. $60 once buys ownership and repetition: export each taxpayer's dated schedule and penalty working as a .csv you keep, and set browser reminders fourteen days before every filing date. Testing one person, the free version finishes the job. Testing forty clients and then remembering four dates each is where the schedule is the thing you needed.

Thresholds and test years: GOV.UK, "Find out if and when you need to use Making Tax Digital for Income Tax".