Ask most tradies what a job cost them and you'll get a rough number, a shrug, or a "we'll find out at tax time." That last one is the problem — by the time the accountant's crunched the numbers, the job's long finished, the client's paid, and there's nothing left to do about a margin that got eaten by an unplanned skip bin and a supplier price hike.
Job costing means tracking what a specific job actually costs, in real time, against what you quoted — not reconstructing it from bank statements three months later. It's not extra bookkeeping. It's the same receipts you're already collecting, just tagged to a job instead of thrown in the ute's centre console.
What job costing actually means for a tradie
One habit, repeated every time money leaves your account or your wallet on a job: tag it to that job, not a general "materials" bucket. Do it consistently and you get a live, job-by-job picture of spend versus quote — instead of finding out you underquoted after the invoice has already gone out.
The costs that quietly eat your margin
- Materials & merchant runs — timber, fixings, sparky and plumbing parts, paint. Easy to track on one big Bunnings run, easy to lose across three small ones.
- Fuel & vehicle costs — ute running costs between sites, claimed via the logbook method or cents-per-kilometre.
- Subbies — anyone brought in to help on a job, whether they're invoicing you with an ABN or not.
- Plant & equipment hire — excavators, scaffolding, generators — day-rate costs that belong to one job, not the business generally.
- Consumables & PPE — blades, screws, sealant, hi-vis, gloves. Small, constant, rarely tracked properly.
- Tool replacement — the drill that walked off site, the blade that snapped mid-cut.
None of these look big on their own. Add them up across a job and they're often the gap between a healthy margin and a job that barely broke even.
Spreadsheet vs app
| Method | Set-up effort | What actually happens |
|---|---|---|
| Glovebox / shoebox | None | Receipts fade in the sun, get lost, no job-level view ever. |
| Spreadsheet | Medium | Works for a week, then dies the first time you're too tired to update it after a ten-hour day. |
| Full bookkeeping software | High | Built for a desk, not a job site. Too many steps mid-job. |
| Purpose-built app (like Site Wallet) | Low | Snap the receipt, tag the job, done in under 10 seconds. |
A worked example: bathroom reno
Say you quote a bathroom reno at $8,500, budgeting $2,800 in materials and $1,200 for a plumber subbie. If every receipt gets tagged to "Bathroom — Nguyen" as it happens, by invoicing time you already know: materials ran to $3,150 after a supplier price rise, plus $180 in unplanned skip hire. That's $8,500 quoted against $4,530 in tracked job costs — a real margin, not a guess made once the client's already paid and moved on.
What the ATO actually wants from you
- ABN and business records — as a sole trader, accurate income and expense records support your annual tax return and are the difference between claiming what you're entitled to and guessing.
- GST registration — required once your turnover reaches $75,000 (or you expect it to). Once registered, GST-compliant tax invoices matter for every job cost you want to claim credits on.
- BAS (Business Activity Statement) — usually lodged quarterly if GST-registered, reporting GST collected and GST credits claimed on business purchases.
- PAYG instalments — regular prepayments toward your expected tax bill, based on your income.
- Vehicle claims — either the cents-per-kilometre method (capped, simpler) or the logbook method (requires a 12-week logbook and actual running costs, but can claim more).
- Record-keeping period — generally five years from when you lodge the relevant return.
This isn't tax advice — thresholds and rules change, so check ato.gov.au or your accountant for your situation. But whatever the current numbers, the habit stays the same: capture the receipt when it happens, tag it to the job, and let BAS time be a formality instead of a scramble.
Mistakes that wreck job costing
- Mixing personal and business spending on one card, meaning every receipt needs manual sorting later.
- No per-job tagging — a single "materials" total tells you nothing about which job actually made money.
- Reconstructing the logbook after the fact — the ATO expects contemporaneous records, and memory rarely does you favours anyway.
- Losing receipts before BAS — thermal receipts fade fast, especially left in a hot ute.
- Never checking actual cost against the quote — the value of tracking is catching an overrun while there's still time to act.
How Site Wallet does this without extra admin
Snap a receipt and Site Wallet's AI reads the vendor, total, date and GST off it in about two seconds — faded thermal receipts included. Tag it to a job in one tap and watch a live, running per-job total build itself, so you can see a job's cost against its quote without touching a spreadsheet. Come BAS time, export a PDF summary, a CSV for your bookkeeping software, or a ZIP of every receipt photo — five years of records kept safe either way.
FAQ
Do I need job costing if I don't have a crew?
Yes, arguably more so — as a one-person operation there's no one else catching a job running over budget. Job-level totals are how you know which jobs are actually worth quoting for again.
How long do I need to keep records?
Generally five years from when you lodge the relevant tax return, though some records (like those related to CGT assets) need to be kept longer.
Does cash spent on a job still need tracking?
Yes. Cash spent on materials or subbies is still a business cost, and cash received is still assessable income — both sides need recording.
Cents-per-kilometre or logbook — which is better for job costing?
Cents-per-kilometre is simpler but capped at a set number of kilometres per year. A logbook takes more upfront effort (a 12-week sample period) but can capture a bigger claim if you're doing genuinely high business kilometres.