Job Costing for Builders: A Simple 4-Step System
The short answer
Job costing means setting a budget for every job from your quote, logging every real cost against it each week, and comparing the two at the end. It tells you which jobs make money while you can still do something about it.
- Budget from the quote: the same cost lines you priced become the budget for the job.
- Log every cost to a job: labour, subcontractors, materials, plant, skips. Nothing goes to "general".
- Check weekly, not at the end: cost to date + cost to complete against the budget, 15 minutes every Friday.
- Close out every job: quoted margin vs actual margin, and why. Feed the real numbers back into your rates.
Most builders find out whether a job made money when the final payment lands, or when the accountant does the year-end. By then it's too late to fix anything, and too late to learn which jobs to stop taking.
Job costing fixes that. It isn't accounting software or a finance degree. It's a budget per job, a habit of logging every cost against it, and 15 minutes a week to compare. Here's a simple job costing system for builders. If you want it set up for your jobs, book a free strategy call.
Why job costing matters more than your annual accounts
Your accounts tell you the business made 4% last year. They don't tell you that bathrooms made 25%, extensions made 2% and one loft lost £6,000. Job costing does.
Here's a real example from our electrical playbook: a rewire quoted at 30% gross margin came in at 19%. A consumer unit job quoted at 35% came in at 38%. Without job costing, both just disappear into "turnover". Most of the gap usually traces back to hidden costs that never made it onto the quote.
Step 1: turn your quote into a budget
If you priced the job properly, the budget already exists. The cost lines in your estimate become the budget lines for the job.
| Cost line | Budget: £60,000 refurbishment |
|---|---|
| Own labour (hours × true hourly cost) | £13,500 |
| Subcontractor packages (electrics, plumbing, plastering) | £16,000 |
| Materials | £11,800 |
| Plant, skips, scaffold | £1,900 |
| Prelims: protection, parking, supervision | £1,800 |
| Total budgeted cost | £45,000 |
| Price (ex VAT) | £60,000 |
| Budgeted gross margin | 25% |
The example is illustrative. If your quote is one lump sum with no cost breakdown, start there: you can't track against a budget that doesn't exist. See how to price building work line by line.
Still finding out what a job made only at the end?
Book a free call with our team. We'll look at how you price and track jobs, and the numbers to check every week.
Step 2: log every cost to a job
Give every job a short reference, such as the address or a number. Then nothing gets spent without it.
- Labour: hours per person per day, against the job. A simple timesheet or a WhatsApp photo of a sheet is enough to start.
- Materials: the job reference on every merchant order and invoice. Ask your merchants to print it.
- Subcontractors: each package's agreed price, what's been paid and what's left.
- Plant, skips, scaffold: hire start and end dates, per job.
- Variations: each one priced and logged separately, so extra work brings extra budget.
Putting costs into "general" or "stock". Every litre of paint and every hour that isn't logged to a job makes that job look better than it is, and another one worse.
Step 3: check every live job weekly
Every Friday, fill in three numbers per cost line for each live job. Cost to date, honest cost to complete, and the forecast total against budget.
| Cost line | Budget | Cost to date | Cost to complete | Forecast | Over / under |
|---|---|---|---|---|---|
| Own labour | £13,500 | £8,200 | £7,100 | £15,300 | −£1,800 |
| Subcontractors | £16,000 | £9,000 | £7,000 | £16,000 | £0 |
| Materials | £11,800 | £7,900 | £3,600 | £11,500 | +£300 |
| Plant and prelims | £3,700 | £2,100 | £1,900 | £4,000 | −£300 |
| Total | £45,000 | £27,200 | £19,600 | £46,800 | −£1,800 |
The table is an illustrative week-4 check. The forecast margin has slipped from 25% to 22%, and the cause is labour. In week four you can still act: re-plan the remaining days, fix the crew to the job, or price variations that were done without paperwork.
- Cost to complete is priced task by task, not a gut feel.
- Any line 5% or more over budget gets a reason and an action.
- Margin on every live job is compared with what you quoted.
- Unsigned extras are listed and priced before next week.
Want help setting up job costing that actually gets used?
Book a free strategy call.
Step 4: close out every job
When the final invoice goes out, spend 20 minutes on a close-out:
- Quoted vs actual margin: the one number that tells you if the job worked.
- The biggest variance: which line went over, and why.
- Hours per item: how long did the plasterboard, the tiling, the first fix really take?
- Update your rates: put the real numbers into your rates library, so the next price is better.
- Decide: do more of this kind of job, re-price it, or stop doing it.
After ten close-outs you'll know which work makes you money. After twenty, your quotes will be built on your own real numbers, not memory.
The spreadsheet: columns that work
You don't need software to start. One file, one tab per job, the same columns every time:
| Column | What goes in it |
|---|---|
| Date | When the cost happened |
| Cost line | Labour, subcontractor, materials, plant, prelims, variation |
| Description | "Plasterer: first floor skim", "Merchant: timber order" |
| Supplier or person | Who you paid |
| Amount (ex VAT) | The cost |
| Budget line total | From the quote |
| Running total | Formula: sum per cost line |
| Variance | Budget minus forecast |
Add a summary tab that pulls the forecast margin from every live job onto one screen. That's the one you look at on Friday. With more than three or four jobs running and other people logging costs, job-management software saves time. But the habit matters more than the tool.
What this changes
Job costing is the difference between "I think we did all right" and knowing. It's also the base for everything else. You price from your own rates, choose which work to chase, and know when you can afford staff. Want help setting up the numbers for your business? Book a free strategy call.
Ghennadi, a decorator from Northampton, went from £2K to £13.5K a month profit in 60 days, largely by pricing jobs properly and presenting quotes live. Pricing properly starts with knowing what your jobs really cost.
£2K to £13.5K a month profit in 60 days
Ghennadi, decorator: pricing jobs properly and presenting quotes live. Individual results, not typical or guaranteed.
Sviat Jay runs a working construction company, Craftex, and mentors owners one-to-one on their own numbers, so the fixes fit your business. Most owners see results in about four months. To see your weakest area in 4 minutes, take the free Construction Business Scorecard. For the five numbers to check every Friday, see our construction business KPIs guide.
The Cash Flow & Margin Blueprint
Includes the job profit calculator, a payment schedule template and a 4-week cash forecast. 15 pages, free.
Get the free guideJob costing checklist
This is general information from a contractor's experience, not financial advice. For your situation, speak to your accountant. On the tools and under £500K a year? Watch our free training first.
Before you go
- Every quote has cost lines that become the job budget
- Every cost carries a job reference
- Every live job gets a 15-minute check on Friday
- Every finished job gets a close-out: quoted vs actual margin
- Real hours and costs go back into your rates library
