5 estimate mistakes that quietly kill construction margins
Change orders, labor padding, and the contingency line you're skipping.
Construction margin gets squeezed from every direction — materials costs, labor hours, customer expectations, and scope that grows after kickoff. But most margin problems start before the first tool comes out of the truck: in the estimate.
Mistake 1: Not separating labor and materials
Lumping labor and materials into a single line item makes it nearly impossible to see where the job went over. When a job loses margin, you need to know whether it was materials cost, labor hours, or both. Separate them from day one.
Mistake 2: Forgetting the contingency line
Field conditions, weather, subcontractor delays, permit revisions — something always goes sideways. Jobs without a contingency line don't account for this; they just erode margin when the inevitable happens.
Standard practice is 10–15% contingency on residential, more for complex commercial. Build it in as a visible line, not a hidden buffer inside other numbers.
Mistake 3: Using round labor numbers
Estimating 40 hours for a task when it realistically takes 52 is how jobs lose 30% of their margin before they start. Track actual hours on every completed job and use those numbers — not optimistic round figures — as your next estimate baseline.
Mistake 4: Ignoring change orders
Scope creep without documentation is a gift to the customer and a loss for you. Every verbal 'while you're there, can you also...' is a change order. Document, price, and get written approval before the work happens. Not after.
Mistake 5: No post-job review
Finishing a job and immediately starting the next one means you never learn. A 30-minute post-job review comparing estimated vs. actual hours and materials surfaces patterns — the same subcontractor consistently running long, the same material category always coming in over, the same type of job always losing margin.
The Construction Job Costing Workbook is built to make all five of these visible: separate labor and materials columns, a contingency line, bid vs. actual comparison, change-order log, and a closeout tab for post-job review.