ESTIMATING ERRORS THAT KILL CONSTRUCTION MARGIN — FIVE SPECIFIC MISTAKES.
The five estimating errors that most consistently destroy project margin all have one thing in common: they are invisible at bid time. The overhead rate looks right. The labor burden multiplier is what it has always been. The general conditions number is what was used last time. The subcontract markup is standard. None of these are examined critically at bid time because the estimate template has not been updated. The losses are locked in before the first crew day. The post-mortem at closeout identifies the gap but cannot recover it.
SPM corrects estimating accuracy by building the data infrastructure that makes accurate estimates possible: documented unit costs from completed projects, an annually recalculated overhead rate, and a general conditions checklist that catches every site cost before the bid goes out.
SPECIFIC ESTIMATING MISTAKES THAT LOCK IN LOSSES BEFORE THE FIRST CREW DAY.
Overhead Underbidding — Applying Last Year's Rate to This Year's Cost Structure
The overhead rate used in bidding should match the current cost of running the business — not last year's rate, not the rate from three years ago when the company was smaller, not the rate a competitor mentioned at an association meeting. A contractor who grew from $2M to $4M and added two PMs, a truck, and an office manager without recalculating the overhead rate is bidding at 11% when the real rate is 17%. Every bid submitted at 11% has 6 points of overhead unrecovered. On a $400,000 project, that is $24,000 in overhead that the job will never produce. The margin shortfall is baked in before mobilization.
Labor Burden Assumption Outdated or Incorrectly Applied
Most estimators use a labor burden multiplier — 1.30, 1.35, 1.42 — applied to base wages to get fully burdened labor cost. When that multiplier is outdated, the estimate is wrong on every labor line. Workers comp rates change at renewal. Health insurance costs increase annually. New hires change the average burden composition. A multiplier that was correct two years ago may understate actual burden by 5–8 points today. On a labor-intensive project with $280,000 in base labor, a 6-point burden understatement is $16,800 in unrecovered labor cost built into the bid.
Mobilization and General Conditions Estimated at Zero or Minimum
Mobilization cost — equipment transport, site setup, temporary utilities, first-week overhead — and general conditions — site office, porta-potties, dumpsters, safety signage, cleanup — are routinely underestimated because they feel like minor items compared to the core scope. On a 5-month $700,000 project, real general conditions run 2–5% of contract value, or $14,000–$35,000. When the estimate shows $4,000 in general conditions, the first month burns through the general conditions budget and every subsequent month of site overhead comes from project margin.
Subcontractor Markup Insufficient to Cover Coordination and Risk
When a contractor subs out scope — hauling, concrete, surveying — the subcontract cost in the estimate needs to include a markup for coordination overhead, contract risk, and the administrative cost of managing the subcontract relationship. A 5% markup on subcontracted scope that carries meaningful schedule or performance risk is not enough. The risk of a subcontractor failing, performing poorly, or generating back-charges flows to the prime. The markup in the estimate should reflect that risk, not just the administrative cost of cutting the check.
No Escalation Allowance on Multi-Year Projects
A fixed-price contract for a project that will run 18–24 months carries material and labor price risk for the duration. Concrete prices move. Steel moves. Labor rates in competitive markets move at mid-contract when crews can get more elsewhere. An estimate submitted today for a project starting in 9 months and running 18 months covers 27 months of price exposure with no escalation allowance. The standard fix is a 2–5% escalation allowance on material-heavy scope for projects with durations above 12 months.
WHAT AN ACCURATE ESTIMATE REQUIRES — AND WHAT PRODUCES IT.
The historical data connection: The most accurate estimates are built from documented historical unit costs — what the specific crew actually achieves on the specific work type. SPM tracks unit cost from every completed project and feeds that data back into the estimate template annually. Over time, the estimate becomes progressively more accurate because it is built from what actually happened, not what was assumed.
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