Estimating Best Practices · June 11, 2026
10 Common Estimating Mistakes That Quietly Kill Margin
Margin doesn't usually leak from one big mistake. It leaks from ten small ones, on every job, all year. Here are the ones we see most often and the one-line fix for each.
The 10 mistakes
- Pricing labor at burdened-only — forgetting non-billable hours like travel, training, callbacks.
- Skipping a contingency line — and then having no place to absorb the inevitable surprise.
- Carrying allowances as zero — every allowance should carry a realistic placeholder.
- No exclusions list — undefined scope is unpaid scope.
- Copy-paste pricing from a 2-year-old estimate — materials moved 30%.
- Trusting the lowest sub bid — it almost always means a scope gap you'll fund.
- Forgetting bonding, insurance riders, or jurisdictional fees.
- Not pricing demobilization, punch list, and closeout labor.
- Sending the estimate without a payment schedule — every late dollar costs you margin.
- No second-pair-of-eyes review on any bid over your size threshold.
The pattern
Eight of these ten mistakes are scope or assumption problems, not math problems. That's why scope gap discipline and leveling discipline matter so much more than a fancier estimating calculator.
Where to start
Frequently asked questions
- Which estimating mistake costs the most?
- Trusting the lowest sub bid. It almost always means a scope gap the GC ends up funding, and the dollar impact dwarfs most pricing errors.
- How big should my contingency line be?
- Project-dependent, but 3–10% of hard cost is a defensible band. Zero contingency means the first surprise comes straight out of margin.
- Is a second reviewer really worth it on every bid?
- On any bid above your size threshold (often $25k+), yes. A fresh set of eyes catches assumption errors the original estimator is blind to, and the cost is minutes.