June 20, 2026June 2, 2026ConstructionMerranti

Why Builders Need Better Job Costing Before They Can Improve Profit

A builder can have a full diary, strong turnover and a busy team but still not make enough profit.

That usually happens because turnover is not the same as margin. A job might look profitable when quoted, but the margin can disappear once labour overruns, extra materials, subcontractor costs, waste, hire charges, snagging, finance costs and unpriced variations are included.

The key point is this: builders cannot improve profit properly until they know which jobs are actually making money.

Job costing gives construction businesses that visibility. It shows the real cost of each project, not just the total sales and total expenses for the year. For builders, this can be the difference between being busy and building a profitable business.

For regular reporting and construction management information, see Merranti’s Financial & Management Accounts page.

What is job costing?

Job costing means tracking income and costs by individual project.

Instead of only asking, “Did the business make a profit this month?”, job costing asks, “Did this specific job make a profit?”

For a builder, job costing may include:

quoted price
agreed variations
labour costs
subcontractor costs
materials
plant hire
tool hire
waste disposal
fuel and travel
site overheads
insurance allocation
project admin time
retentions
snagging
rework
final gross margin

A construction business that does not track these costs by job may not know which work is profitable and which work is quietly losing money.

Suggested future internal blog link once published: Construction Accounting: Common Tax and Cash Flow Issues Builders Face

Why turnover is not enough

Many builders measure success by turnover. That is understandable, but it can be misleading.

A business turning over £800,000 with weak margins may be less profitable than a business turning over £500,000 with stronger job control. Higher turnover can also increase pressure if the business needs to fund more materials, more subcontractors and more VAT or CIS admin.

Turnover shows the value of work sold. It does not show whether the work was priced correctly or delivered profitably.

A builder should be able to answer:

Which jobs made the highest margin?
Which jobs lost money?
Which customers create the most delays?
Which types of work are hardest to price?
Are labour hours being estimated accurately?
Are materials being marked up properly?
Are variations being charged?
Are retentions affecting cash flow?
Are subcontractors reducing or improving margin?

Without job costing, these questions are often answered by instinct rather than evidence.

Suggested future internal blog link once published: Why Your Profit Is Not the Same as Your Cash in the Bank

Job costing helps improve quoting

Accurate quotes depend on accurate historic cost data.

If previous jobs were not costed properly, future quotes are based on rough assumptions. This can lead to underpricing.

A strong quote should consider:

expected labour hours
hourly or daily labour cost
subcontractor rates
materials
waste allowance
plant and equipment hire
travel and fuel
disposal costs
site-specific complications
overhead recovery
target profit margin
VAT treatment
CIS position, where relevant
contingency for delays or variations

The best pricing decisions are based on actual job results, not memory.

For example, if kitchen extensions consistently take 15% more labour than quoted, the business needs to know that before pricing the next one. If bathroom refurbishments produce better margins than general repair work, that should influence marketing and quoting.

Labour costs need to be tracked properly

Labour is one of the biggest cost areas for builders.

If labour time is not tracked by job, profitability can be badly distorted. A project may look profitable because materials were controlled, but labour overruns may have wiped out the margin.

Builders should track:

hours worked by employees
director or owner labour time
subcontractor labour
overtime
travel time
time spent fixing mistakes
snagging time
unpaid quoting or design time
project management time

Owner time is often ignored. This is a problem. If the owner is working long hours on site but the job only makes a small profit, the business may not be charging enough.

For payroll support where labour costs are growing, see Merranti’s Payroll page.

Materials can quietly reduce margin

Material costs can change quickly, especially in construction.

A quote prepared several weeks before work starts may not reflect the final price paid for timber, steel, plasterboard, electrical materials, plumbing supplies or specialist items.

Job costing should track:

quoted material budget
actual material spend
supplier invoices
delivery charges
wastage
unused materials
customer upgrades
materials charged as variations
supplier price increases
credit notes and returns

If material overruns are not tracked, the business may keep repeating the same quoting mistakes.

Builders should also check whether materials are being allocated to the correct job. If materials are posted to general purchases only, the accounts may show total cost but not job-level profit.

Suggested future internal blog link once published: What Expenses Can a Limited Company Claim? A Practical Guide for UK Directors

Subcontractors and CIS affect job profitability

Subcontractor costs need to be recorded accurately by job.

This is especially important where CIS applies. GOV.UK explains that contractors deduct money from subcontractor payments and pass it to HMRC, with deductions counting as advance payments towards the subcontractor’s tax and National Insurance. It also confirms that CIS covers most construction work to buildings, structures and civil engineering works. Useful outgoing link: GOV.UK: Construction Industry Scheme overview.

If a builder uses subcontractors, the job cost report should show:

subcontractor invoice value
labour and materials split
CIS deduction
net payment
VAT treatment
job allocation
payment date
retention or dispute status

Poor CIS records can distort job cost reports and create tax problems.

Suggested future internal blog link once published: CIS Tax Explained for Subcontractors and Contractors

VAT and reverse charge can affect reporting

VAT should not be confused with profit.

Construction businesses need to know whether VAT is being charged, reclaimed or handled under domestic reverse charge rules.

GOV.UK’s VAT domestic reverse charge guidance states that the reverse charge applies to many standard and reduced-rate construction services reported within CIS, where the businesses are VAT registered in the UK. It also says businesses should make sure accounting systems and software can deal with the reverse charge and check the cash-flow impact. Useful outgoing link: GOV.UK: VAT domestic reverse charge for construction.

VAT does not usually form part of profit in the same way as sales income, but incorrect VAT treatment can distort accounts and cash flow.

A job costing system should make it clear:

whether the customer is VAT registered
whether VAT is charged normally
whether reverse charge applies
whether materials include recoverable VAT
whether VAT affects the customer-facing price
whether VAT cash has been reserved

For VAT support, see Merranti’s VAT Services page.

Suggested future internal blog links once published:

VAT Registration: When It Becomes Compulsory and When It Might Be Worth Doing Early
Should I Register for VAT If I Am Below the Threshold? Pros and Cons

Variations should be priced and recorded

Unpriced variations are a major reason construction margins disappear.

A customer asks for extra work. The builder agrees to “sort it”. The team does the work. Materials and labour increase. But the final invoice does not fully recover the extra cost.

Job costing helps identify whether variations are being captured.

A proper variation process should record:

what changed
who requested it
estimated extra labour
extra materials
subcontractor impact
VAT treatment
agreed price
customer approval
invoice status
payment status

Without this process, extra work becomes free work.

Builders should avoid relying on memory. Variations should be documented before the work is done wherever possible.

Retentions and delayed payments affect the real result

A job may show a profit but still damage cash flow if money is held back.

Retentions, delayed stage payments and customer disputes should be tracked by job.

A retention tracker should show:

customer or main contractor
job reference
invoice number
retention amount
due release date
defects period
amount received
outstanding balance
dispute notes

Retentions affect the real cash result of a job. If they are not tracked, they can be forgotten, delayed or treated as if they are already available.

Suggested future internal blog link once published: How Construction Businesses Can Improve Cash Flow Without Just Chasing More Work

Overheads need to be recovered in pricing

Job costing should not only include direct costs.

A construction business also has overheads, such as:

insurance
accounting fees
software
phone
vehicle finance
storage
rent
marketing
admin wages
office costs
training
subscriptions
professional fees

If jobs are priced only to cover labour and materials, the business may not recover enough overhead to make a proper profit.

A builder should know their monthly overhead base and build overhead recovery into pricing. Otherwise, every job can appear profitable individually while the business still struggles overall.

For regular overhead review and forecasting, see Merranti’s Financial & Management Accounts page.

Job costing helps decide what work to stop doing

Not every job is worth taking.

A builder may discover that certain jobs create low margins, slow payments, difficult customers or too much rework.

Job costing can help identify:

most profitable job types
least profitable job types
customers that regularly delay payment
jobs with frequent variations
work that takes too much owner time
trades or subcontractors affecting margin
materials that are often underestimated
types of work that create cash-flow strain
Improving profit is not always about doing more. Sometimes it is about doing less of the wrong work.

Job costing needs accurate bookkeeping

Job costing only works if bookkeeping is reliable.

If supplier invoices are missing, subcontractor costs are posted to the wrong job, VAT codes are wrong or labour is not tracked, the job costing report will not be useful.

The accounting system should be set up to record:

project codes
supplier bills by job
subcontractor costs by job
materials by job
direct labour by job
stage invoices
deposits
retentions
variations
VAT treatment
CIS deductions

For software setup support, see Merranti’s Accounting Software and Cloud Accounting pages.

Suggested future internal blog link once published: The Accounting Checklist Every Growing Construction Business Needs

What a good job costing report should show

A useful job costing report should be simple enough for the builder to use.

It should show:

job name
customer
quoted value
variations
total invoiced
labour cost
subcontractor cost
material cost
plant and hire costs
other direct costs
total direct cost
gross profit
gross margin percentage
cash received
cash still due
retention amount
expected completion margin

This report should be reviewed during the job and after completion. If it is only reviewed months later, the business loses the chance to act.

Practical job costing checklist for builders

Before starting a job, check:

Has the quote included labour, materials, subcontractors and overhead?
Is there a target gross margin?
Are payment terms agreed?
Is a deposit needed?
Are stage payments clear?
Does CIS apply?
Does VAT or domestic reverse charge apply?
Are materials priced using current supplier costs?
Are variations documented before work starts?
Is the job set up in the accounting system?

During the job, check:

Are labour hours tracking against budget?
Are materials over budget?
Have variations been priced and approved?
Are subcontractor invoices correct?
Are stage invoices being raised on time?
Is cash being received as expected?
Are retentions being tracked?
Are unexpected costs being recorded?

After the job, check:

What was the final gross margin?
Did labour exceed the estimate?
Did materials exceed the estimate?
Were variations fully charged?
Did the customer pay on time?
Was the job worth taking?
What should change before quoting similar work again?

Useful further reading and links

Useful outgoing GOV.UK links:

How Merranti can help

Better job costing gives builders clearer information about profit, pricing and cash flow. It helps show which jobs make money, which jobs drain cash and where quoting needs to improve.

Merranti Accounting can help construction businesses set up accounting software, track job costs, review margins, manage CIS and VAT, prepare management accounts and forecast cash flow.

If you want clearer job profitability reporting, visit Merranti’s Financial & Management Accounts page, see Limited Company Accounting, or contact Merranti to discuss your construction business.

FAQ

What is job costing for builders?

Job costing is the process of tracking income and costs by individual construction project. It helps builders see which jobs are profitable after labour, materials, subcontractors, plant, overheads and variations are included.

Why is job costing important in construction?

Job costing is important because a builder can be busy without making enough profit. It shows where margins are being lost and helps improve future quoting.

What costs should be included in construction job costing?

A job costing report should usually include labour, materials, subcontractors, plant hire, tool hire, waste disposal, fuel, travel, variations, retentions and an allocation for overheads.

Does CIS affect job costing?

Yes. CIS affects subcontractor payments and deductions. Subcontractor labour, materials splits, CIS deductions and net payments should be recorded accurately by job.

Can job costing improve cash flow?

Yes. Job costing can highlight jobs where materials, labour, retentions or late payments create cash-flow pressure. It helps builders price and manage jobs more effectively.

Can Merranti help builders with job costing?

Yes. Merranti can help builders set up job costing reports, management accounts, cash-flow forecasts, CIS records, VAT treatment and accounting software.