BQ vs Actuals: Job Costing That Tells the Truth on Site
The bill of quantities is a promise made at tender; the site is where the promise meets reality. Job costing is the discipline of comparing the two while the job is still running — the difference between a correction you can make and a loss you can only absorb.
Every construction project begins with a bill of quantities — a line-by-line schedule of the materials, labour, and work the job requires, priced to produce the tender. Once the contract is signed, that price is fixed. From that moment the entire game is cost: every shilling spent above the BQ allowance for a line comes directly out of margin, and every shilling saved is margin kept. Job costing is simply the practice of tracking what you actually spend against what the BQ said you would — and the only version of it that matters is the one that happens while the job is still running.
Committed, not just spent
The mistake most contractors make is tracking only money already paid. By the time a cost is paid it is ancient history. Real job costing tracks three numbers against each BQ line: the budget (what the BQ allowed), the committed cost (purchase orders raised and subcontracts let, whether or not paid), and the actual cost (materials consumed and work done). Committed cost is the one that gives you warning: the moment you raise POs for steel that exceed the BQ steel allowance, the line is over-committed, and you know it before a single invoice arrives. Tracking only actuals is like driving by the rear-view mirror.
Cost against progress, not the calendar
A line being 50% spent is meaningless on its own — it is good news at 70% complete and a crisis at 20% complete. Useful job costing compares cost incurred against work actually completed, so an overrun is measured against progress. This is where site materials discipline pays off: because material issues are booked against tasks, you can see that the foundations consumed 130% of their concrete budget at completion, flag it, and protect the remaining pours — instead of learning at handover that concrete as a whole ran over and having no idea where.
| Number | What it tells you | When it warns you |
|---|---|---|
| Budget (BQ) | What the line was priced to cost | Baseline — set at tender |
| Committed | POs and subcontracts raised, paid or not | Earliest — before invoices arrive |
| Actual | Material consumed and work done | As the work happens |
| Actual vs % complete | Whether spend matches progress | While there is still job left to fix |
Variations: the margin most contractors give away
The BQ is not the whole story — clients change their minds, ground conditions surprise, and scope grows. Every variation is either extra revenue you claim or extra cost you absorb, and the difference is documentation. Contractors who log variations against the job as they arise — instructed, priced, and claimed — recover them. Contractors who "sort out the variations at the end" discover that memory, goodwill, and missing paperwork have quietly converted claimable work into free work. Job costing that captures variations as first-class events, not end-of-job reconstruction, is where a surprising amount of lost margin actually hides.
The report that runs a contract
One report, per job, updated as work flows: each BQ line with its budget, committed, and actual cost, the variance, and cost against percentage complete — plus logged variations. A contractor who reads this weekly manages a project; one who sees it only at the final account is reviewing a post-mortem. The information is worthless the day after you could have acted on it.
Live job costing is the payoff for the rest of the contractor's operational discipline. It needs materials booked against tasks, procurement flowing through approved POs, and subcontracts and variations logged as they happen — the same connected operations that the wider construction guide describes. Assemble those, and the gap between the promise and the reality stops being a year-end surprise and becomes a number you steer by.
Cost every job while it still runs
See budget, committed, and actual against every BQ line, cost measured against progress, and variations captured as they arise.
Explore construction operationsFrequently asked questions
What is BQ vs actual job costing?
It is the practice of comparing what a construction job actually costs against what its bill of quantities budgeted, line by line, as the work runs. Because the contract price is fixed at tender, any spend above the BQ allowance comes out of margin — so tracking actual against budget in real time is what lets a contractor catch and correct an overrun before it becomes a loss.
Why track committed cost and not just money spent?
Because paid cost is history. Committed cost — purchase orders raised and subcontracts let, whether or not yet paid — warns you the moment you commit to spend above a BQ line, before any invoice arrives. Tracking only actuals means you always learn about overruns too late to do anything about them.
How do variations affect job costing?
Variations are changes to the contracted scope — each is either revenue you can claim or cost you must absorb. Contractors who log and price variations as they arise recover them; those who leave them to the end routinely lose claimable work to missing paperwork and fading memory. Capturing variations as they happen is where a lot of hidden margin is saved.
Do I need special software for job costing?
You need materials booked against tasks, procurement flowing through approved POs, and costs tracked against BQ lines on one connected system — that is what makes live job costing possible. A spreadsheet can hold the BQ, but it cannot see committed cost accumulating or material consumed against progress in real time, which is exactly where the value is.
