MTD and your January Self Assessment return

Grace is fictional, but the moment she is in will be familiar to landlords who joined MTD for Income Tax in its first wave. She has been sending quarterly updates through her software since the summer, so when her accountant mentions a January Self Assessment deadline, her first reaction is that MTD was supposed to have replaced that. It has not, not yet, and understanding why turns on which tax year each deadline actually belongs to.

Two tax years are genuinely running at once

Grace’s MTD quarterly updates cover the 2026/27 tax year, the first one she has been mandated for. The January deadline her accountant means is for the 2025/26 tax year, the one that finished the day before MTD started for her. That earlier year predates her mandation, so it was never reported through quarterly updates at all; it still needs an ordinary Self Assessment return, filed the way returns always have been.

Both years carry a real deadline, and neither replaces the other. The overlap exists only because MTD started partway through the annual filing cycle, not because anything has gone wrong.

The ordinary return covers the year before MTD started

The online Self Assessment return for the 2025/26 tax year is due by 31 January 2027. Nothing about that deadline changed when MTD began; it follows HMRC’s ordinary Self Assessment timetable, filed for the whole 2025/26 year using the records kept before quarterly reporting existed for people like Grace.

There is no MTD software requirement for this particular return, because MTD for Income Tax did not apply to the 2025/26 tax year. Grace can file it the way she always has, whether that is HMRC’s online service, her existing accounting software, or through her accountant, using whatever records she kept for that year.

The MTD year running underneath has its own, later deadline

Her 2026/27 quarterly updates, covering the tax year that began on 6 April 2026, feed into a separate year-end step: the tax return for the 2026/27 tax year, due by 31 January 2028, a full year after the 2025/26 return. That is where the four quarterly updates for2026/27 are drawn together, allowances are claimed, and the actual tax position for that year is settled. The first quarterly update guide explains what those four updates involve and when each one falls due; the main MTD guide covers the wider threshold and eligibility rules.

What to do in the meantime

Two separate jobs are running side by side. File the 2025/26 return by its own deadline using the records for that year, and keep sending the 2026/27 quarterly updates against their own schedule on the deadlines calendar. The two do not need to be done in any particular order relative to each other, since they draw on different records and answer to different deadlines. What matters is treating each as its own task rather than assuming progress on one clears the other.

Questions people ask about the two deadlines

Why are two different tax deadlines both live during my first MTD year?

Because MTD started partway through the annual filing cycle. Your last pre-MTD tax year still needs an ordinary Self Assessment return on its usual January deadline, while your first MTD tax year runs its own quarterly updates and a later year-end step.

Does my January return for 2025/26 need to go through MTD-compatible software?

No, not for that particular return. MTD for Income Tax did not apply to the 2025/26 tax year, so you can file it the way you always have; MTD software becomes relevant for the 2026/27 return and the quarterly updates that lead up to it.

Does filing my 2025/26 return early let me skip anything in 2026/27?

No, the two are independent. Finishing the 2025/26 return early does not reduce or replace any of the 2026/27 quarterly updates, which still need to be sent on their own schedule regardless of when the earlier return is filed.

Where do I find the exact dates for my 2026/27 quarterly updates?

The deadlines calendar lists the standard and calendar quarterly periods for every tax year in the mandate, including 2026/27, alongside the return deadline that follows them. The first quarterly update guide walks through what each of those updates needs to contain.