Estimating mistakes that eat your margin

Most margin is lost at the estimating desk, long before anyone notices on site. The mistakes below come up again and again in builders’ own stories. None of them is hard to fix once you see it.

1. Pricing off a square metre rate

A square metre rate ignores slope, access, cladding, room mix and the shape of the house. A New Zealand estimating guest says similar-sized houses from one group builder swung 10 to 15% on the rate just from a change in shape.¹ On a custom home or a renovation, that swing is bigger than your whole net profit.

Do this instead: use a rate only as an early budget check with the customer. Price the contract from a full takeoff.

2. Using allowances where you should measure

Plastering “should be about this much”, electrical “roughly that much”. Package allowances feel quick, but the real quantities only appear when someone does the takeoff again at purchase order stage. If they come in higher, the difference comes out of your margin.²

Do this instead: build the bill of quantities first, then apply your own rates, preliminaries, overheads and margin. Quantities such as rough-in points or metres of stormwater have one right answer. Keep them separate from your rates so trades price a clear scope.²

3. Guessing labour hours

Labour is where jobs blow out. One guest puts labour hours at about 80% of a job’s profitability and recommends forecasting hours by stage to within 5%.¹ A New Zealand builder allowed about 8,000 hours on one large job and the crew took about 13,000, with a contract that gave no room to pass on rising costs.³

Do this instead: build labour up stage by stage, ask your foreman for his own estimate, and track hours used against hours allowed while the job runs. Feed the results into the next quote.

4. Quoting off last year’s prices

Prices move between quote and build. CoreLogic’s Cordell index showed material costs up 30.8% from the start of COVID to late 2024. A $5,000 underestimate sounds small until it repeats across twelve jobs and becomes $60,000.⁴

Do this instead: check your price file against current supplier notices before every quote, keep a log of each price rise you receive, and keep quote validity short.

If a number in your estimate came from memory or an old job, check it against a current price before the quote goes out.

5. Thin allowances on unknown ground

A $2,000 pier allowance on a site with uncontrolled fill turned into a $35,000 variation once the engineering came back.⁵ A variation that size strains the relationship with the customer even when the contract allows it, and if it does not, you wear it.

Do this instead: get a geotechnical report before contract on any site with fill, slope or doubtful soil. Set provisional sums from site information and tell the customer the realistic range. Provisional sum rules differ by state, so check what applies where you build.

6. Shaving the price to win

You put the price together, it looks too high, so you take 10% off. A Queensland builder says he did exactly that early on and won jobs that made no money. He now shows site costs such as toilet hire and fencing as lines in his quote and uses estimating software with labour schedules.⁶

Do this instead: if the price looks high, recheck the quantities and rates. If they hold, the price is right. Lose the job rather than take it at a loss.

7. Rushing the takeoff

A Melbourne builder priced a job at eleven o’clock at night, tired and with sick kids at home. The job ran six weeks and returned nothing, and he honoured the price anyway.⁷ His rule now is to ask the customer for another day rather than rush.

Do this instead: book estimating time in daylight hours, and have a second person check the takeoff and the spreadsheet formulas on any job of real size before it goes out.

Where to next

Once the estimate is sound, make sure the margin on top of it is right. Read Margin vs markup, then Top 10 ways to improve your margin.

Footnotes

1. Nick Clements, “If You Quote Jobs Like THIS You Will Run Out Of Cash”, The Professional Builder (podcast), 2026. https://www.youtube.com/watch?v=_o7LWHrTn00 ↩ ↩²

2. The Good Builder, “The Hidden Cost of Guesswork: Why Allowance Based Estimating Is Killing Margins”, The Good Builder, 2025. https://thegoodbuilder.com.au/the-hidden-cost-of-guesswork-why-allowance-based-estimating-is-killing-margins/ ↩ ↩²

3. Martin and Helen, “Stop ‘Guessing’ Labor Hours: How To Fix Massive Profit Leaks”, The Professional Builder (podcast), 2026. https://www.youtube.com/watch?v=RbMwSpTQbP4 ↩

4. The Good Builder, “Why Good Builders Still Lose Money”, The Good Builder, 2026. https://thegoodbuilder.com.au/why-good-builders-still-lose-money/ ↩

5. The Good Builder, “What Your Building Contract Is Telling Clients Before You Even Meet Them”, The Good Builder, 2026. https://thegoodbuilder.com.au/what-your-building-contract-is-telling-clients-before-you-even-meet-them/ ↩

6. Jimmy Gray, “Built With Heart. Jimmy Gray on Family, Craft and What It Really Takes to Be a Good Builder”, The Good Builder Podcast, 2026. https://www.youtube.com/watch?v=weNXI30HWBY ↩

7. The Good Builder, “Melbourne Builder Phil Del Titto Finished His Apprenticeship Without Ever Seeing a Purchase Order. He Says the Gap Still Has Not Closed.”, The Good Builder, 2026. https://thegoodbuilder.com.au/melbourne-builder-phil-del-titto-finished-his-apprenticeship-without-ever-seeing-a-purchase-order-he-says-the-gap-still-has-not-closed/ ↩