Plumbing · method first, fictional example below

Which plumbing jobs make the most money?

There is no ranking that holds for every firm. It depends on your prices, how long each job takes your engineers, how often jobs need a return visit, and whether you are short of work or short of engineers. Work out two figures for each type of job, profit per job and profit per engineer hour, and use the one that matches your constraint. In the fictional example below, bathroom installations earn the most per job and the least per engineer hour.

Why invoice size misleads

A big invoice is mostly other people's money

In the example, the average bathroom installation invoice is £5,300 and the average servicing visit is £160. But 58% of the bathroom installation revenue goes straight out to suppliers and subcontractors, against 5% for servicing. What is left then has to pay for the engineer hours, and big jobs use a lot of them.

Per engineer hour, servicing leaves £66.62 after materials and labour. Bathroom installations leave £13.37.

The method

Five steps, the same for every job type

01Group the jobsUse the types you already book under: callouts and repairs, servicing, boiler installations, bathrooms. Four to six groups is enough; one job belongs to one group.
02Take off what passes throughRevenue excluding VAT, less materials and subcontractors bought for those jobs.
03Charge the hoursEvery engineer hour the jobs used, including travel and return visits, at what those hours cost you. What is left is the contribution.
04Share the overheadsVans, office, premises and marketing, each by what drives it. This is the step that most often reorders the ranking.
05Divide twiceBy jobs and by engineer hours. Then decide which of the two matters for the constraint your firm actually has.

Each step is worked through in pounds, with the overhead rules compared side by side, in how to calculate profit by job type.

Fictional example · Harbour Plumbing & Heating · 2025

Four plumbing job types, two ways of ranking them

Job type	Jobs	Average invoice	Contribution per job	Contribution per engineer hour	Profit per hour	Return visits
Boiler replacements	68	£2,650	£316.42	£14.34	£4.47	11 (16%)
Repairs & call-outs	620	£239	£106.62	£37.77	£12.88	46 (7%)
Bathroom installations	25	£5,300	£615.05	£13.37	£3.99	7 (28%)
Servicing	430	£160	£100.71	£66.62	£30.27	14 (3%)

An invented five-person firm: owner on the tools, three engineers and one office coordinator. GBP excluding VAT. Contribution is revenue less materials, subcontractors and field labour; profit also takes off overheads shared by cost driver. Engineer hours include return visits; travel is recorded separately. This is an example, not a UK or US benchmark. Every job behind it is in the example report.

Ranked per job: bathroom installations, then boiler replacements, then repairs & call-outs, then servicing. Ranked per engineer hour: servicing, then repairs & call-outs, then boiler replacements, then bathroom installations. A firm with engineers waiting for work should care most about the first list. A firm turning work away should care most about the second.

When the ranking changes

Four things that move it

Your constraint

If you are short of engineers, rank by the hour. If you are short of enquiries, rank by the job and by total profit, and ask whether the high earners per hour have enough demand to fill the diary.

Return visits

7 of 25 bathroom installations (28%) needed a second visit. Those hours belong to the original job. Unrecorded, they make the type look better than it is.

A small number of jobs

There were only 25 bathroom installations. The worst one lost £1,078. Without it, profit per job would be £236.01 instead of £183.44. Look at the individual jobs before trusting an average built from a few dozen.

Price

Holding jobs and costs the same, a 5% price rise on boiler replacements adds 42% to their contribution; on servicing, 8%. Where most of the invoice passes through to suppliers, a small change in price makes a large change in what is left. Whether customers accept it is a separate question.

What to export

The records that answer the question

From your job softwareJob number, date, job type, customer type, invoice total excluding VAT, engineer, time on site, travel time, and any return visit linked to the original job.

From purchasingSupplier invoices or purchase orders with the job number they were bought for, and subcontractor invoices the same way.

From payrollAnnual cost of each engineer: wages, employer's National Insurance or payroll taxes, pension, overtime.

From the accountsThe year's overheads by heading: vehicles, premises, office staff, software, insurance, marketing, tools.

Choosing one service to look at

From the ranking to one decision

Take the type that ranks highest on the measure for your constraint and check three things: that it has enough jobs behind it to trust, that its hours include travel and return visits, and that there is demand for more of it in your area. If all three hold, that is the work to quote for more readily, and the work your website and reviews should point at.

Take the type at the bottom and check its hourly price against your floor rate and the plumbing pricing guide. Change one thing for a quarter, then run the numbers again. The job type calculator does the first three steps in a minute.

For how a Nelvant report does this across up to five years of a plumbing firm's jobs, see UK plumbing and heating or US plumbing.

Find out which of your jobs pay.

£400 / $500 · up to 5 years of your jobs · 5 working days · refunded in full if nothing material is found

Your own job history, every type ranked per job and per engineer hour, with the assumptions written down and checked by a person.

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