Making Tax Digital
What does it take to integrate with HMRC’s APIs?
There are good engineering write-ups of HMRC’s APIs. Almost all of them end with a working sandbox integration and leave the reader believing production is one switch away. It is not, and the gap is measured in working days you have not planned for.
The step the walkthroughs skip
HMRC’s own wording: “We’ll check your application, which takes up to 10 working days.” Only if the request succeeds can you generate production credentials.
The sequence is: register on the Developer Hub, build against the sandbox with test credentials, create a production application, subscribe it to the APIs you want, then apply for production credentials and agree to the terms of use. The review sits between you and going live, and it is not mentioned in any of the popular technical guides.
There is a second, separate approval if you want to describe the product as recognised: the “MTD ready — recognised by HMRC” trademark, requested by form and email, which HMRC says it typically processes within 3 to 5 working days. All software on HMRC’s compatible-software finder has been through its recognition process — though HMRC is careful to add that it does not recommend any product or provider.
One thing I cannot tell you: whether any of this costs money. No HMRC page I could reach states a fee, and none states that it is free. Several of the current Developer Hub terms pages are not publicly fetchable. Treat the cost as unknown rather than zero.
Who has to do this, and when
| Qualifying income | Tested on the return for | Must start |
|---|---|---|
| Over £50,000 | 2024-25 | 6 April 2026 — already in force |
| Over £30,000 | 2025-26 | 6 April 2027 |
| Over £20,000 | 2026-27 | 6 April 2028 |
The £20,000 band was confirmed in a policy paper of March 2026 and brings an estimated 970,000 additional people into scope. For VAT the position is simpler and already settled: all VAT-registered businesses have been in scope since 1 April 2022, when the below-threshold exemption was removed.
The requirement that shapes the architecture
HMRC’s rule on digital links is the one that decides how you build. Where data moves between the programs that maintain the electronic account, it must travel over a digital link. HMRC states plainly that manual re-keying is not acceptable, and that copy and paste does not count.
In practice that rules out the spreadsheet-in-the-middle pattern a lot of finance teams actually use, unless the spreadsheet is itself linked. If you are building for clients with existing workflows, this is the conversation to have in week one rather than at recognition.
HMRC also specifies the records that must be kept digitally: designatory data, time and value of supplies made and received split by VAT rate, input tax claimed, summary totals, and each adjustment type as its own total.
The penalties your users are exposed to
Worth knowing even if you are only building the software, because it is what your customers will ask about.
| Late submission | Threshold | Penalty |
|---|---|---|
| MTD for Income Tax | 4 points | £200, then £200 per further missed deadline |
| VAT, quarterly | 4 points | £200, then £200 each |
| VAT, monthly | 5 points | £200, then £200 each |
| VAT, annual | 2 points | £200, then £200 each |
One point per missed deadline, even if the taxpayer runs several businesses, and Income Tax points are separate from VAT points. There is a concession worth knowing for the first year: HMRC states there are no penalties for missing a quarterly update deadline in 2026-27. From 2027-28 a missed quarterly update earns a point. The quarterly deadlines are 7 August, 7 November, 7 February and 7 May.
Late payment is where the numbers moved. On 1 April 2025 the VAT late payment penalties rose from 2% and 2% to 3% at day 15 and 3% at day 30, and the second penalty from an annual rate of 4% to 10%, charged daily from day 31. The MTD for Income Tax regime mirrors that shape, at 3% in 2026-27 and 4% from 2027-28, with a 30-day grace period in the first year rather than the usual 15.
What HMRC does not publish
- How many compatible products exist. HMRC removed the published software tables on 31 July 2025 and replaced them with a dynamic finder, so there is no total. A page quoting a product count is quoting something that no longer exists.
- Sign-up numbers for MTD for Income Tax. HMRC’s developer newsletters describe volumes as within expected ranges and give no figures.
- End-to-end recognition time, beyond the 10-working-day credentials check and the 3-to-5-day trademark request.
The planning consequence is simple enough: between a working sandbox integration and a recognised production product there are at least two HMRC-side waits you do not control, and neither is long individually. They just are not in anybody’s estimate.
Sources. Production credentials and the review step: HMRC Developer Hub, getting started. Recognition and the trademark route: GOV.UK, choosing software for Making Tax Digital for Income Tax, last updated 13 July 2026, and HMRC’s MTD for Income Tax software developer newsletter, edition 3, 29 May 2026. Mandation dates: GOV.UK eligibility guidance, last updated 26 March 2026, and the policy paper reducing the threshold to £20,000, 24 March 2026. VAT scope, digital links and record requirements: VAT Notice 700/22, and SI 2021/986, in force 1 April 2022. Penalties: GOV.UK guidance on penalties for Making Tax Digital for Income Tax, published 12 March 2026 and updated 30 March 2026; VAT penalty points guidance; and the policy paper increasing late payment penalty rates, 1 April 2025, amending Schedule 26 to the Finance Act 2021. All retrieved 9 October 2026. This is a description of published material, not tax advice.
Building something that files to HMRC?
The approval gates and the digital-link rules shape the architecture more than the API does. Worth getting right before you build, rather than at recognition.
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