Profit margin is the percentage of money left after costs have been taken out of a job. For builders, it is not just an accounting number. It affects whether a job is worth taking, whether the business can cover overheads, and whether a quote leaves enough room for risk.
This guide explains how to calculate profit margin in plain terms, how it differs from markup, and how to use the Cost Estimator profit margin calculator without confusing margin, overhead and contingency.
Want to check the numbers quickly?
Use the profit margin calculator to test your cost, selling price, margin and markup before finalising a quote. It is useful for quick checks, but it still depends on the costs being complete.
Profit margin formula
The basic profit margin formula is:
Profit margin = (profit ÷ selling price) × 100
Where:
- Profit = selling price minus total costs
- Selling price = the amount charged to the client
- Total costs = labour, materials, plant, preliminaries, subcontractors, overhead recovery and other allowed costs
Example:
- Total cost: £80,000
- Selling price: £100,000
- Profit: £20,000
- Profit margin: £20,000 ÷ £100,000 × 100 = 20%
That means 20% of the selling price is profit. It does not mean the builder added 20% markup to the cost.
Profit margin vs markup
Margin and markup are often mixed up. They are related, but they are not the same thing.
- Markup is added to cost.
- Margin is measured against the selling price.
If a job costs £80,000 and you add 25% markup, the selling price becomes £100,000. The profit is £20,000. The margin is 20%, not 25%.
This difference matters because a builder who confuses markup with margin can think a job is more profitable than it really is.
Construction profit margin example
Take a small renovation job with these estimated costs:
- Labour: £28,000
- Materials: £22,000
- Subcontractors: £14,000
- Plant, skips and access: £4,000
- Preliminaries and supervision: £7,000
- Total cost: £75,000
If the builder quotes £90,000, the profit is £15,000.
Profit margin = £15,000 ÷ £90,000 × 100 = 16.7%
If the builder wanted a 20% margin, the selling price would need to be higher. The calculation would be:
Required selling price = cost ÷ (1 – target margin)
For a £75,000 cost and a 20% target margin:
£75,000 ÷ 0.80 = £93,750
The difference between £90,000 and £93,750 may decide whether the job is worth taking.
Do not calculate margin from incomplete costs
The margin formula is simple. The hard part is making sure the cost figure is complete.
Before using the calculator, check whether the estimate includes:
- labour time and realistic productivity
- materials, waste and delivery
- subcontractor costs
- plant, equipment and small tools
- site setup and welfare
- supervision and management time
- insurance, compliance and documentation
- access, protection, skips and waste
- risk allowances or provisional sums
- overhead recovery
A margin calculation based on an incomplete cost is false comfort. The spreadsheet may show profit, but the job can still lose money once the missing items appear.
Where overhead fits
Overhead is not the same as profit. Overhead is the cost of running the business: office time, vehicles, software, insurance, finance costs, admin, management and other costs that are not always tied neatly to one job.
Some builders recover overhead through a percentage added to each job. Others build it into labour rates or preliminaries. Either approach can work, but it needs to be deliberate.
If overhead is ignored, the quoted margin can look healthy while the business still struggles to make money.
Where contingency fits
Contingency is an allowance for uncertainty. It should not be treated as profit. If the contingency is used up dealing with unclear scope, access problems or design changes, it is no longer available as margin.
For clearer quote control, separate:
- fixed measured work
- provisional sums
- prime cost allowances
- risk allowances
- profit and overhead
This makes the quote easier to explain and reduces the chance that the builder accidentally gives away risk for free.
How to use the profit margin calculator
Use the calculator when you want to check one of three things:
- what margin a proposed selling price gives you
- what selling price is needed for a target margin
- how markup and margin compare on the same cost base
It works best when the estimate has already been built properly. If the job costs are still rough, use the calculator as a benchmark rather than a final pricing decision.
Open the profit margin calculator.
When estimating support helps
Estimating support is useful when the margin calculation depends on a cost base that has not been measured properly yet.
For example, if a builder has drawings and a rough scope but no time to measure quantities, separate preliminaries or check allowances, Cost Estimator can help prepare a clearer estimating basis before the quote is finalised.
That is especially useful where:
- the job has several trades
- the client needs a fixed or better-qualified quote
- there are drawings but no clear bill of quantities
- material and subcontractor exposure needs checking
- the builder needs to decide whether the job is worth pricing at all
For related pricing discipline, see maximising profit margins with accurate cost estimation and keeping assumptions and exclusions clear before the quote goes out.
FAQs
What is a good profit margin for building work?
There is no universal figure. A good margin depends on business overhead, job risk, competition, payment terms, project size and how complete the estimate is. The important point is to calculate margin from a realistic cost base, not a rough guess.
Is 20% markup the same as 20% margin?
No. A 20% markup on cost produces a lower margin when measured against the selling price. Margin and markup use different denominators, so they should not be used interchangeably.
Should contingency be included in profit margin?
No. Contingency is an allowance for uncertainty or risk. Profit margin is what remains after the job costs have been covered. Treating contingency as profit can make the job look safer than it is.
Why does profit disappear even when the quote included margin?
Usually because the original cost base missed something, the scope changed, allowances were too low, preliminaries were underpriced, or the quote did not make exclusions clear enough.
Next step
If you only need a quick calculation, use the profit margin calculator. If the cost base itself needs checking from drawings, scope or tender information, see estimating support for builders.
