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Making Tax Digital

Why your second MTD update looks twice as big as your first

· Updated · 10 min read · Checked against GOV.UK guidance on 6 November 2026 (guide last updated 16 October 2026) and HMRC's quarterly update direction of 27 March 2026

Why is my second update roughly double the first?

Because it covers twice as long. If you were expecting the July-to-October quarter on its own, the number can look as if you have accidentally counted your rent twice.

You have not. HMRC is explicit about it.

“Each quarterly update covers from the start of the current tax year (6 April) to the end of the update period.”

GOV.UK, Use Making Tax Digital for Income Tax: send quarterly updates, updated 16 October 2026

So the second update is not the July-to-October quarter. It is April to October. The third is April to January. The fourth is the whole year. Where your rent comes in evenly, each one looks proportionally larger than the last, and the last one looks like your annual figure, because it is.

What a year of updates actually looks like

The chart below shows the same landlord under both models: what people expect (four separate quarters) against what MTD actually asks for (a running total). Figures are illustrative, at £2,000 of rent a month.

£0£24k£6kUpdate 1£12kUpdate 2£18kUpdate 3£24kUpdate 4What people expect (per quarter)What MTD asks for (cumulative)
Illustrative only, at £2,000 rent per month. The cumulative figures are what you actually submit. Source for the cumulative model: GOV.UK, send quarterly updates.

How do I correct a mistake in an earlier update?

You correct your records as soon as possible and send the correction in your next update. This is the part that turns the cumulative model from a curiosity into the best thing about MTD.

Because every update restates the year from its start (6 April on standard periods, usually 1 April on calendar periods), and because, in HMRC's own words on its developer hub, “each update invalidates the previous submission”, a wrong figure in your first update is simply overwritten by the right one in your second. There is no separate amendment for an earlier quarterly update, because the design does not need one.

Two caveats worth having. Fixing the digital record is not optional. The law requires this: you must correct the digital record as soon as possible and send the correction by your next update, or for the fourth update by your tax return deadline (SI 2026/336 reg 17). And if the error is in your fourth update, there is no fifth to overwrite it, so you resend the fourth or adjust the category total in your software. GOV.UK is explicit about this: you may need to resend your fourth quarterly update to correct an error, to add jointly-let property expenses you left out of earlier updates, or to record Rent-a-Room income, and you should do it before you make any tax adjustments and before you submit your tax return. Mechanically, resending is the same PUT to the same record. It is only “an amendment” in the sense that you are writing the year again. Once you have submitted your tax return, the route changes: you amend the return itself through your software, within 12 months of the submission deadline.

What this looks like from inside the HMRC API

The API is the clearest proof that the cumulative model is real rather than a presentational quirk.

For 2025-26 onwards, HMRC's API has no separate record for each quarter. You still send an update by each quarterly deadline, but in the Property Business (MTD) API v6.0, the old period-summary endpoints (create and amend a UK property income and expenses period summary) stopped accepting data for tax years 2025-26 onwards. They still exist, and still serve the years up to 2024-25, but for the current regime they are dead. They were replaced by a single cumulative period summary, released to production in v5.0 on 14 April 2025, carried into v6.0. (v6.0 is published as beta, last updated 20 October 2026.)

What replaced them is one path, supporting exactly two verbs:

PUT /individuals/business/property/uk/{nino}/{businessId}/cumulative/{taxYear}

GET the same path to read it back.

Read that path again. It is keyed by National Insurance number, business ID and tax year. The quarter is not part of the key at all. There is one record per UK property business per tax year, and every update is a PUT that overwrites it. Amending is not a different operation. It is the same operation, again.

When people describe MTD as “four submissions”, the API disagrees: it is one record, normally written at least four times.

We built LetSort against this endpoint and test it daily in HMRC's sandbox. On 29 October 2026 HMRC gave LetSort production access, which lets it connect to HMRC's live systems. That does not make it HMRC recognised, and we do not claim otherwise. As at 8 November 2026 no filing has gone through LetSort's live service, and the full filing journey has only run in HMRC's test environment. LetSort covers UK property income only. HMRC's press release of 12 August 2026 says quarterly updates need to be sent through HMRC-recognised software. The regulations say “functional compatible software” (SI 2026/336 reg 3). LetSort is not recognised or listed, so if you need to file now, choose a product from HMRC's finder and check it is available now.

GOV.UK says you can send each update any time from the end of the update period to the update deadline, or up to 10 days before the period ends if you do not expect to record any further transactions in it. You can still send it after the deadline, but it is late. GOV.UK says a late update normally earns a penalty point, but HMRC will not apply points to late quarterly updates during 2026-27. If you missed 7 November, that covers your second update. The next deadline is 7 February 2027. Whenever you send it, it restates the year.

A practical note if you are watching for it. HMRC can take up to an hour to mark an obligation as fulfilled after you submit. If you filed on the afternoon of 7 November and saw “open” ten minutes later, that was not necessarily a failure.

The update periods, written the way HMRC actually means them

If a deadline table shows discrete windows (6 July to 5 October and so on), that is not how HMRC's current guidance shows them: what you send for each deadline runs from the start of the year.

The Income Tax (Digital Obligations) Regulations 2026 (SI 2026/336, in force 1 April 2026) define each quarterly update period as running from a ‘relevant start date’ to the quarter end. On standard periods that is 6 April (reg 12), or 1 April if you used calendar periods the year before. On calendar periods it is 1 April, or 6 April if you are switching from required standard updates (reg 13). The 2026 Regulations replaced earlier rules (SI 2021/1076 as amended by SI 2024/167) that never came into force.

UpdatePeriod coveredLengthDeadline
Update 16 Apr to 5 Jul 20263 months7 Aug 2026
Update 26 Apr to 5 Oct 20266 months7 Nov 2026
Update 36 Apr 2026 to 5 Jan 20279 months7 Feb 2027
Update 46 Apr 2026 to 5 Apr 202712 months7 May 2027

The table shows standard update periods. Calendar update periods end on 30 June, 30 September, 31 December and 31 March, usually starting 1 April, with the same deadlines.

Because a calendar period ends earlier but its deadline does not move, each period ends five days further from its deadline. That is not a free extension: GOV.UK says to use calendar periods if your accounting period covers 1 April to 31 March, and HMRC tells software not to offer them to anyone else. The choice is made per business in your software, before your first update of the year. After that update you cannot change it for the rest of the tax year, and it carries forward until you change it. Standard or calendar update periods covers how to choose.

What actually goes in an update, and what does not

Totals, by category, and nothing clever. GOV.UK is blunt about it: “You do not need to make any accounting or tax adjustments before sending a quarterly update.” Capital allowances, private-use adjustments and claims for reliefs or allowances that reduce your taxable property income are adjustments you may make after your fourth update, before you submit your tax return. If your total UK property turnover is under £90,000 (the VAT registration threshold) you can categorise your records in less detail for that tax year. With more than one self-employment or UK property income source, each must be under the threshold. If you have UK residential property income you must still record residential finance costs separately and send them separately.

There is one trap here, and until July 2026 an article on this blog fell into it.

Mortgage interest is reported quarterly. The relief is not.

HMRC's quarterly update direction lists Residential property finance costs and Residential finance costs brought forward as quarterly reporting categories for a UK property business. So you do report your mortgage interest every quarter. What happens at year end is the relief: since Section 24, residential finance costs are not deducted from profit. They give a tax reduction at the basic rate (20% for 2026-27; from 2027-28 Finance Act 2026 gives the relief at the property basic rate, which Budget 2026 announced at 24%, to be legislated in Finance Bill 2026-27. The Budget rates apply in England, Wales and Northern Ireland; if you pay Scottish income tax, check how this applies to you), worked out on the lower of your finance costs (including any brought forward), your property profits (after any brought forward losses) and your adjusted total income: income after losses and reliefs, excluding savings and dividend income, above your personal allowance. The reduction cannot create a tax refund. Unused costs carry forward to later years of the same property business. That is applied in the year-end calculation. Finance costs on loans not related to a dwelling are a separate category and are not restricted in this way. A loan covering both is apportioned on a just and reasonable basis, and since 2025-26 furnished holiday lets are restricted in the same way as other residential lets.

The practical consequence: HMRC's guidance does not say whether the in-year estimate reflects mortgage interest relief, so do not rely on it to show it. If you read that finance costs are left out of quarterly updates and handled only at year end, that conflates reporting with relief. You report quarterly. You get relieved annually.

Common questions

Are MTD quarterly updates cumulative or per-quarter?

Cumulative. GOV.UK states: "Each quarterly update covers from the start of the current tax year (6 April) to the end of the update period." Your second update therefore runs 6 April to 5 October on standard update periods (1 April to 5 October if you used calendar periods the year before), or usually 1 April to 30 September on calendar periods.

Why is my second MTD update roughly double my first?

Because it covers twice as long. The first update runs 6 April to 5 July and the second 6 April to 5 October on standard periods (both start on 1 April if you used calendar periods the year before); on calendar periods usually 1 April to 30 June and 1 April to 30 September. Where rent comes in evenly, six months of income is roughly double three months of income. The figure is not an error and you have not double-counted.

How do I correct a mistake in a previous MTD quarterly update?

You do not need a separate amendment. The law requires you to correct your digital records as soon as possible (SI 2026/336 reg 17), then you include the corrected figures in your next cumulative update, which supersedes the previous one. HMRC states that each update invalidates the previous submission. If the error is in your fourth update, there is no fifth to overwrite it. GOV.UK gives two routes: correct the record and resend the fourth update, or adjust the category total in your software and reflect it in your digital records. Do either before you submit your tax return. If you resend, do it before you make any tax adjustments. If you have already submitted your tax return, change the return through your software instead, within 12 months of the submission deadline.

Does HMRC’s API still have a separate record for each quarter?

Not for 2025-26 onwards. You still send quarterly updates by each deadline, but in the Property Business (MTD) API v6.0 they all go to one cumulative period summary per UK property business per tax year, created and amended with a PUT. The legacy period-summary endpoints still exist for tax years up to 2024-25, but they do not accept data for 2025-26 onwards. The record is keyed by National Insurance number, business ID and tax year, so the quarter is not part of the key at all.

Is mortgage interest reported in MTD quarterly updates?

Yes. HMRC’s quarterly update direction lists "Residential property finance costs" and "Residential finance costs brought forward" as quarterly reporting categories for a UK property business. The reporting is quarterly. What happens at year end is the relief. For residential property, finance costs give a tax reduction at the basic rate (20% for 2026-27; from 2027-28 Finance Act 2026 gives the relief at the property basic rate, which Budget 2026 announced at 24%, to be legislated in Finance Bill 2026-27. The Budget rates apply in England, Wales and Northern Ireland; if you pay Scottish income tax, check how this applies to you), worked out on the lower of your finance costs (including any brought forward), your property profits (after any brought forward losses) and your adjusted total income: income after losses and reliefs, excluding savings and dividend income, above your personal allowance. The reduction cannot create a tax refund. Unused costs carry forward to later years of the same property business. Finance costs on loans not related to a dwelling are a separate category and are not restricted in this way. A loan covering both is apportioned on a just and reasonable basis, and since 2025-26 furnished holiday lets are restricted in the same way as other residential lets. HMRC’s guidance does not say whether the in-year estimate applies this relief, so do not rely on the estimate to show it.

Do calendar quarter update periods have different deadlines?

No. Calendar update periods shift the data periods (usually 1 April to 30 June, and so on) but the deadlines stay at 7 August, 7 November, 7 February and 7 May, so each period ends five days further from its deadline. They are not a free extension: GOV.UK says to use them if your accounting period covers 1 April to 31 March, and HMRC tells software not to offer them to anyone else. The choice is made per business in your software, before your first update of the year. After that update you cannot change it for the rest of the tax year, and it carries forward until you change it.

Sources

Primary sources first.

Related

Missed the 7 August or 7 November MTD deadline? There is no penalty, but you still have to send the update covers the penalty position for 2026-27.

Written by Ben Morton, founder of LetSort. I build our HMRC Making Tax Digital integration directly against the API: OAuth, fraud prevention headers, and the cumulative period summary described above. When this article says HMRC's API has no separate record for each quarter from 2025-26, that is not only a reading of the documentation: that is what our software talks to in HMRC's sandbox. On 29 October 2026 HMRC gave LetSort production access, which lets it connect to HMRC's live systems. That does not make it HMRC recognised, and we do not claim otherwise. LetSort is not on HMRC's software list. As at 8 November 2026 no filing has gone through LetSort's live service, and the full filing journey has only run in HMRC's test environment. LetSort covers UK property income only. LetSort is operated by ToggleKit Ltd.