How should a gas engineer quote and invoice?

A good quote wins the job. Invoicing well gets you paid for it. Most engineers are sharper on the first than the second, and it shows in the bank: work finished in March, money landing in May. This is a simple system for the whole loop.

Quote or estimate: what's the difference?

A quote is a fixed price for a defined piece of work. Once the customer accepts it, you have generally agreed to do that work at that price, so if the job runs over, you carry the cost. An estimate is your best guess, and the final bill can come out different. Customers blur the two words. The document shouldn't. Say which one it is, in writing.

The practical rule: quote when you can see and scope the work, like a boiler swap you have surveyed. Estimate when there are genuine unknowns, like tracing a leak under a screeded floor, and say what would change the number. Quoting a job full of unknowns is how you end up working a second day for free.

What should a gas engineer's quote include?

• Scope: exactly what you will do, in plain words. If it isn't written down, the customer will assume it's included.
• Exclusions: what you won't be doing, such as making good plaster, disposing of the old appliance, or electrical work beyond the appliance connection.
• Materials and labour, split out. A single lump sum invites haggling; a split shows where the money goes.
• A validity window, commonly 30 days, so a price given in July can't be claimed against winter parts prices.
• Payment terms: when payment is due, how the customer can pay, and any deposit.

That one page protects both of you. Most disputes on domestic work are about what each side thought was included, and a clear scope with exclusions settles the argument before it starts.

How do you price the quote from your day rate?

Start from your costed day rate, not from what you reckon the customer will stand. If you haven't worked yours out, do that first; the day rate guide walks through it. Fuel, insurance, van, software, registration and training all sit inside that number. Then price the labour as days at your rate, add materials at what they actually cost you plus a consistent handling margin, and add a line for any risk you flagged in the survey.

If the number feels high, resist trimming it to win the job. A quote priced below your day rate is you paying to work, and losing a job you would have lost money on is a good outcome.

When should you ask for a deposit?

Take a deposit whenever you're ordering materials you can't easily return, or blocking out more than a day or two of diary. A deposit that covers the boiler and parts means a cancellation doesn't leave you owning someone else's cylinder. On small repairs and service visits most engineers don't bother.

Keep it proportionate and state it on the quote. Contracts agreed in a customer's home can carry cancellation rights, so written terms protect you if the customer changes their mind after you've committed to materials.

How and when should you invoice?

Same day, every time, and ideally from the doorstep before you drive off. An invoice sent while the customer is still pleased with the work gets paid faster than one written up from a duplicate pad at the end of the month. Treat sending it as the last task of the job, not an evening chore.

GOV.UK sets out what an invoice must include, and it's a short list:

• A unique invoice number.
• Your name (plus any business name) and address, and the customer's name and address.
• A clear description of the work, the date it was done and the invoice date.
• The amounts charged, VAT if you're VAT registered, and the total due.

Add your payment details and terms, and if you can take a card payment on the spot, offer it. Paid on the doorstep beats any payment terms you could write. The card payments guide covers the options.

Which payment terms actually get you paid?

For domestic work, “due on receipt” is reasonable and normal. Nobody gives a homeowner 30 days to pay for a boiler service; 30-day terms are a habit imported from commercial contracts. If due on receipt feels blunt, 7 days is a fair compromise. For letting agents and commercial clients, 14 or 30 days is often their standard, so agree terms before the work starts, not on the invoice.

Whatever you choose, print it on the quote and repeat it on the invoice. A term the customer never saw isn't a term, it's a wish.

What can you do about late payers?

There's now a tax reason to run all of this in software too. Making Tax Digital started in April 2026 for sole traders with gross income over £50,000, meaning digital records and quarterly updates to HMRC, with lower bands following in 2027 and 2028. If your invoices already live in software, MTD is close to a non-event. The Making Tax Digital post covers the deadlines.