Site Diary — Downloadable
Budget Calculator
A five-sheet Excel workbook built around one question most owner-builder advice skips: not can you do it yourself, but whether doing it yourself actually saves you money once your time, your delays and your risk of getting it wrong are counted.
The question it answers
Say a painter quotes $12,000. Materials would cost you $3,500, tools $900, and it'll take you 90 hours over four weeks instead of their two. The cash saving looks like $7,000 — that's the number people repeat. Once your time and the extra fortnight of holding costs are counted, the real saving is closer to $1,900, and you're effectively paying yourself about $66 an hour to do it.
That might be an excellent deal or a terrible one — it depends entirely on what your hour is worth, which only you know. The workbook does the arithmetic and hands the judgement back to you.
What's in it
Sheet
Summary
Your assumptions in one place — time value, contingency, holding cost, duration. Everything else in the workbook flows from these five numbers.
Sheet
Budget
42 line items across the five build stages, with budget vs committed vs actually paid, and variance updating live so drift shows up early instead of at the end.
Sheet
DIY or Trade
The one that changes decisions. Counts your hours, tools, waste, extra weeks and the risk of paying someone to fix it — then tells you what you're really earning per hour.
Sheet
Quote Comparison
Four quotes side by side on the same scope, including a line for what each one leaves out. The cheapest headline is rarely the cheapest quote.
Sheet
Document Register
35 certificates, approvals and concealed-work photos tracked by stage. The paperwork is part of the building — missing certificates surface years later, when the trade is gone.
Two things it will not do
- 01Tell you what your build costs. Every dollar figure in it is a placeholder to be overwritten with your own real quotes — none of them are researched market rates, and treating them as benchmarks would be a mistake.
- 02Tell you whether you're any good at the job. It's arithmetic, not judgement. For anything that gets covered up — waterproofing, flashings, structural work — you set the risk figure, and it should reflect how expensive that mistake really is.
Preview the workbook
The real structure and reference content from all 5 sheets, read-only. Unlock to enter your own numbers, see it calculate live, and download the editable .xlsx.
Your five assumptions drive every other sheet. Locked here — enter your own once unlocked.
Project name
Your time value ($ per hour)
If DIY means taking unpaid leave, use your real earning rate. If it's evenings and weekends you wouldn't be earning anyway, use a lower number. This one input changes every answer.
Contingency %
10-15% is commonly suggested. Lower than 10% on a first build is optimistic.
Your finance / holding cost ($ per month)
Interest, rent elsewhere, storage. This is what every month of delay actually costs you.
Planned build duration (months)
Cost roll-up
Trade + materials subtotal, contingency, Long Service Levy, and total project cost all calculate live from the Budget sheet and your assumptions above — locked until unlocked.
Unlock the full calculator
AUD $99 one-time — live-calculating workbook, editable .xlsx download, plus every other paid roadmap stage.
Unlock Full Access →Not legal, financial, tax or professional building advice, and not a substitute for real quotes or a quantity surveyor. The one figure in here drawn from a NSW rule — the Long Service Levy at 0.25% of build cost for works of $250,000 or more — should still be confirmed with the Long Service Corporation before you rely on it.