How do I submit a quarterly update to HMRC as a gas engineer?

Your software sends HMRC turnover and cost totals for the year so far: boiler work, safety checks and CIS installs together, card takings before fees. If you start in April 2027, your first update is due by 7 August 2027.

Making Tax Digital for Income Tax (MTD) asks for totals each quarter, not receipts. A gas engineer's quarter mixes homeowner boiler work, landlord safety checks and builder installs inside the Construction Industry Scheme (CIS), all in one update. Checked against GOV.UK and HMRC's CIS manual on 18 October 2026; the general guide covers everyone.

Who sends them, and when

You join once your self-employment and property income before expenses goes over the line: over £50,000 in 2024-25 meant 6 April 2026, over £30,000 in 2025-26 means 6 April 2027, and over £20,000 in 2026-27 means 6 April 2028. The sign-up guide for gas engineers shows how to add up your jobs.

With accounts to 31 March, GOV.UK says to use calendar periods ending 30 June, 30 September, 31 December and 31 March, chosen in your software, with the same deadlines. A quarter with no income or expenses still needs an update.

Homeowners, landlords and letting agents

CIS 340 says householders are not contractors, so a homeowner pays you in full. In our reading, a landlord who only lets property is not one either unless its construction spending passed £3 million in the previous 12 months. A letting agent acting for one generally is not, but can be if it contracts in its own name.

Landlords must have each gas appliance and flue they are responsible for checked at least every 12 months. In our reading, that check is servicing, which CIS 340 excludes, so safety checks invoiced to an agent are paid and counted in full.

Installs for builders: in CIS or not

CIS changes how you are paid, not whether a job goes in the update. HMRC's manual counts gas as a power supply, and the CIS guide for heating engineers sorts more jobs:

• In CIS: installing a complete heating system or gas supply, as in a new build, or replacing a whole system. CIS 340 says a heating firm or builder paying you for a full system in someone's home must still operate CIS.
• Out on their own: a boiler swap, even for a builder, because the manual says replacing a boiler is not installing a system; also repairs, servicing and an extra radiator.
• Mixed contracts: making good or other building work in the same contract brings every payment under it into CIS.

HMRC's notes say a subcontractor's turnover is the full amount before CIS deductions, so in our reading the gross figure on each monthly payment and deduction statement goes in, not what your bank shows.

Card takings, parts and running costs

Card readers pay out with their fee already taken. GOV.UK says that if you only know your income after expenses, you find the full amount, record it as income and record the expenses separately. HMRC's tax return notes say turnover includes card payments. The card fees guide has more.

In our reading, usual costs go in these totals; the expenses guide for gas engineers lists more:

The law requires self-employed people doing gas work to belong to a class approved by the Health and Safety Executive, so in our reading the Gas Safe fee is a cost of trading, like the trade subscriptions HMRC's notes list there.

Under £90,000 of turnover, GOV.UK lets each record be just income or an expense. Reach £90,000, and the year's records must be fully categorised before your next update.

What stays out of the update

HMRC's quarterly update direction lists the totals an update holds, and CIS deductions are not among them. HMRC adds them to your MTD tax return, and any refund is requested separately through HMRC online services, as the CIS refund guide explains.

A worked example

A gas engineer starts MTD on 6 April 2027. By 5 July 2027, homeowners pay them £6,200 for boiler work, £4,800 by card, and the card provider keeps £84. A letting agent pays £2,400 for 32 safety checks at £75. A developer pays for heating and gas supplies in two new houses: £5,000 labour plus £2,500 for boilers and pipe they bought, taking 20% from the labour only, £1,000. A builder pays £2,100 in full for a boiler swap under a separate contract. Other merchant purchases are £2,900, van costs £620 and analyser calibration £150.

Their bank received £17,116, but their turnover is £18,200. This is an example only.

What this means for you

A mistake is fixed by the next update. If you must use MTD, a late update can earn a point from 2027-28 (joined April 2026) or 2028-29 (joining April 2027, per the 28 October 2026 Budget); 4 points bring a £200 penalty. Compare MTD software for gas engineers.

Steps to send your update as a gas engineer

1. Download card provider statements showing takings before fees.
2. Match safety check invoices to what landlords and agents paid.
3. Collect builders' statements for deductions taken, and chase any missing.
4. Check each builder job, and its whole contract, against the CIS lines.
5. Record homeowner, landlord and card jobs in full, and CIS payments gross.
6. Record merchant receipts, van costs, card fees, calibration and your Gas Safe fee.
7. Send the update from your software by the deadline.
8. After the fourth update, check the CIS deductions HMRC adds to your tax return.

The free MTD check shows when you start, and the trades section has more guides.