MTD for income tax: the heating engineer’s step-by-step compliance guide

Making Tax Digital for Income Tax is live. If your gross turnover from self-employment plus any rental income was above £50,000 in the 2024–25 tax year, you’re in the first wave and need to be set up now. Between £30,000 and £50,000, your date is April 2027.

This guide covers the lot: working out whether you’re in scope, what you submit and when, which software works, and how to keep records straight through the year without it becoming another evening job.

Who is actually affected, and when?

From 6 April 2026, the first wave of 860,000 sole traders and landlords must use digital software to manage their tax affairs. Self-employed electricians, plumbers, builders, roofers and every other trade operating as a sole trader sit squarely in the group HMRC came to first.

The rollout runs in three stages:

April 2026: qualifying income over £50,000
April 2027: qualifying income over £30,000
April 2028: qualifying income over £20,000

The threshold drops to £30,000 from April 2027 and £20,000 from April 2028, eventually bringing up to three million more self-employed people into the digital regime.

HMRC has been clear that even without direct notification, “it is still your responsibility to check if and when you need to use” MTD. A letter isn’t the trigger.

The number that catches most heating and plumbing firms out: qualifying income

Qualifying income is your gross self-employment income, meaning total business turnover or receipts, plus your gross UK property income, meaning total rental receipts. Gross is the word doing the work: total income before any expenses, allowances or reliefs.

Turn over £58,000 with expenses bringing profit down to £32,000, and HMRC is still looking at £58,000. The question isn’t whether you made more than £50,000 profit. It’s whether gross income from self-employment and property went over £50,000.

Take a self-employed gas engineer turning over £45,000 who also rents out an inherited flat for £8,000 a year. Qualifying income is £53,000, so even with a taxable profit of £28,000 they’re over the Phase 1 threshold and comply from April 2026.

Employment income is excluded. A few PAYE shifts alongside the trade don’t count towards the threshold.

How to check your own figure

Your qualifying income comes straight off your 2024–25 Self Assessment return. Using full accounts, it’s Box 9, “Total income from self-employment (turnover)”. Using simplified accounts, it’s the same box: “Your turnover: the total income from your self-employment”. Add gross rental income to that, and the combined figure is what HMRC uses.

What MTD actually requires you to do

The old system was one Self Assessment return a year, by 31 January. Now you submit income and expense summaries every quarter plus a final year-end declaration.

The four quarterly updates

Each update summarises your business income and expenses for the three-month period. No invoices, no receipts, just the totals in each category.

They aren’t mini tax returns, because accounting and tax adjustments are optional at that stage. Each one is the total of each category of income and expense for the quarter.

The deadlines:

Q1 (6 April to 5 July): submit by 7 August
Q2 (6 July to 5 October): submit by 7 November
Q3 (6 October to 5 January): submit by 7 February
Q4 (6 January to 5 April): submit by 7 May

HMRC-approved software is required for these. Spreadsheets alone don’t qualify.

The final declaration

After the fourth quarter you file a Final Declaration by 31 January following the end of the tax year. It replaces the traditional Self Assessment return, confirming total income, claiming reliefs and allowances and finalising your tax liability.

MTD doesn’t change when you pay. It changes how often you report. Quarterly updates are submissions, not bills, and the payment timeline stays as it was.

What if you have multiple businesses or income sources?

Each trade or property business needs its own quarterly update, so a sole trader who also rents out a property makes eight submissions a year. Organise your records with that in mind from the start.

What about penalties?

MTD penalties work on points, like a driving licence. Miss a quarterly update deadline and you get a point. No fine arrives immediately: the fixed £200 penalty lands once you reach the threshold, usually four points for quarterly reporters.

For 2026/27 there’s a soft landing, with no penalty points issued for late quarterly updates in the first year. Late payment penalties still apply, and you won’t accumulate points towards the £200 fine for missed quarterly filings.

From 2027/28 the full system applies: each late update adds a point, and four points means £200.

Annual obligations sit outside the soft landing. A late final declaration or late payment of tax attracts penalties from day one.

The step-by-step compliance checklist

Step 1: Work out your qualifying income. Take your 2024–25 Self Assessment return, find gross turnover from self-employment, add gross rental income. Above £50,000 and you’re in now. Between £30,000 and £50,000 and you’re in from April 2027.

Step 2: Check you’re registered. HMRC won’t sign you up automatically. Register through your Government Gateway account, or ask your accountant to do it through their agent services account.

Step 3: Choose HMRC-compatible software. It needs to connect to HMRC via an API, keep digital records to the required standard, and submit both quarterly updates and the Final Declaration. A spreadsheet only works with approved bridging software behind it.

Step 4: Start keeping digital records. Digital records are required for each source of business or property income, each capturing date, amount and category. Every job you invoice, every bag of materials, every tank of diesel gets logged as you go rather than reconstructed at year end.

Step 5: Submit your first quarterly update by 7 August 2026. It covers 6 April to 5 July 2026, so have your software set up and authorised well before then.

Step 6: File your Final Declaration by 31 January 2028. That covers 2026–27 and replaces your usual Self Assessment return for the year.

Which software do you actually need?

HMRC maintains a list of approved providers. The ones most relevant to heating and plumbing firms are Xero, QuickBooks, Sage and FreeAgent, all of which Mucka integrates with directly.

Xero is a well-established cloud accounting platform, fully MTD-compliant. It connects to your bank, categorises transactions, and lets you or your accountant submit quarterly updates to HMRC. Automating the data entry cuts the scope for human error, and each quarterly update gives you a clearer view of the tax building up.

QuickBooks offers much the same and is equally popular with self-employed engineers, handling both record keeping and HMRC submission in one place.

Either is a solid choice, and the decision usually comes down to what your accountant already uses, which makes the Final Declaration handover smoother.

What about spreadsheets? You can keep records in a spreadsheet, as long as it’s digitally linked to MTD-compliant software that handles the submission. Bridging software is that link.

Where Mucka fits in

The hard part isn’t the software, it’s keeping records current through the year rather than doing a catch-up every three months.

Mucka captures jobs, invoices and expenses as part of the working day, with no separate bookkeeping session. When the quarterly update comes round the figures are already there, clean and categorised, ready to push through to Xero, QuickBooks or FreeAgent.

Four quarterly deadlines on top of a full workload only works if the record keeping is built into the day.

The awareness problem

Research from IPSE and Sage found that of 1,000 sole traders surveyed, only 30% had a clear understanding of what MTD involves. Seven in ten either hadn’t heard of it or didn’t realise it requires digital record keeping and quarterly submissions through approved software.

That tracks with what we hear on the ground. Plenty of firms still assume their accountant handles everything, or that the January Self Assessment deadline is the only date that matters. Neither holds up under MTD.

Sage and IPSE estimate 1.8 million sole traders fall within scope, with 90% not yet on digital platforms.

A few common mistakes to avoid

Using profit instead of turnover to check your threshold. HMRC looks at gross income before expenses. A plumber turning over £60,000 and keeping £22,000 after materials and van costs is in scope for April 2026.

Ignoring rental income. A buy-to-let stacks on top of self-employment turnover. £25,000 of turnover plus £10,000 of gross rent is £35,000 of qualifying income, which puts you in the April 2027 window even though neither stream reaches the threshold alone.

Assuming VAT compliance covers you. MTD for Income Tax applies to your Self Assessment, not your VAT. Being compliant for VAT doesn’t make you compliant for income tax, and you may need to register for the new service separately.

Leaving software sign-up until the deadline. Authorising software to connect to HMRC takes time, and an accountant needs to link through their agent services account. Do it now rather than the week before your first quarterly deadline.

Frequently asked questions

Does MTD change when I pay my tax?

No. It changes how often you report income and expenses. Payment stays on the same January and July payments on account schedule, and quarterly updates are reports rather than demands.

What if my income drops below the threshold after I’ve signed up?

Once you’re in, you generally can’t opt out just because income falls, and you keep sending quarterly updates unless the self-employment and property income cease. If qualifying income stays below the threshold for three consecutive years after joining, you may be able to leave.

Can I use a spreadsheet instead of accounting software?

For the underlying records, yes, as long as approved bridging software connects it to HMRC for the submission. Most firms find a dedicated platform like Xero or QuickBooks simpler than managing a bridging layer.

Do I need to send my invoices and receipts to HMRC each quarter?

No. The quarterly update is a summary of income and expenses by category. Keep invoices and receipts in case of an enquiry, but you don’t submit them.

What if I trade through a limited company?

Trading exclusively through a limited company keeps you outside these rules. There’s no Making Tax Digital for Corporation Tax mandate for 2026, and no date has been set at the time of writing. MTD for Income Tax applies to sole traders and landlords.

Get set up before it becomes urgent

MTD is the biggest change to how heating and plumbing firms report earnings since Self Assessment arrived in the 1990s. The rules are live, the deadlines are fixed, and the soft landing runs out.

Mucka integrates with Xero, QuickBooks, Sage and FreeAgent to keep job records, invoices and expenses organised as part of the working day, so the quarterly deadline isn’t a scramble.