Pricing & estimating
5 Estimating Mistakes That Cost Contractors Money
6 min read
Most contractors don't lose a job's profit in one big mistake. They lose it in small, repeatable estimating errors that quietly stack up across every job and every year.
Here are the five most common ones — and the specific fix for each. None of them require you to charge more; they just require you to stop leaving money on the table.
Mistake 1 — Confusing Markup with Margin
This single math error causes contractors to systematically underprice without ever realizing it. Markup is a percentage of your cost; margin is a percentage of your price. They are not the same number.
Mark up $10,000 of cost by 20% and you get a $12,000 price — but that's only a 16.7% margin, not 20%. If you assume the two are interchangeable, every quote you build comes in lower than you think. The fix is to price from the margin you need: Price = Cost ÷ (1 − target margin). We break this down in detail in how to price a job correctly.
Mistake 2 — Estimating Labor Hours Optimistically
Almost everyone underestimates how long a job will actually take — especially anything with unknowns: opening a wall, working around an older electrical panel, dealing with whatever the last contractor left behind.
Optimistic labor estimates feel competitive when you're bidding, but they're the fastest way to turn a profitable job into a break-even one. The fix is to track actual hours against estimated hours on every job, then adjust your future estimates with that real data instead of hoping the next one goes faster.
Mistake 3 — Leaving Overhead Out of the Price Entirely
Many contractors price using only labor and materials, then treat whatever's left as "profit." But that leftover still has to cover insurance, vehicle costs, tools, software, and admin time before any of it becomes real profit.
Overhead typically runs 10-20% of revenue. If it isn't baked into your pricing, you're not as profitable as your jobs make you feel — and you may be effectively working for free once the bills are paid. Price overhead into every job, not as an afterthought.
Mistake 4 — Doing Extra Work Without a Signed Change Order
The "while you're here" requests are relentless, and each one feels too small to formalize. But across a job — and across a year — that unbilled work adds up to real money done for free.
This is one of the most common and most fixable margin leaks in the trades. The fix is simple: document and price every addition as a signed change order before you do it. For the full workflow, see how to manage change orders without losing profit.
Mistake 5 — Never Comparing Estimated vs Actual After the Job
This is the meta-mistake — the one that lets all the others repeat forever. If you never compare what you quoted to what the job actually cost, you can't learn from a single job you've ever done.
Contractors who track estimated vs. actual consistently improve their estimating accuracy significantly within a year, because every job becomes data for the next quote. Contractors who don't keep making the same misjudgment indefinitely.
Frequently asked questions
Why do contractors underbid jobs?
+
Usually for two reasons: they confuse markup with margin (so the math is off before they start), and they estimate labor hours optimistically. Both push the price below what the job actually costs, and without tracking estimated vs. actual, the contractor never finds out why the money disappeared.
How do I stop doing free work on change orders?
+
Treat every 'while you're here' request as a priced change order and get it signed before you do the work. The moment you do extra work on a verbal yes, your leverage is gone. A simple rule — no signature, no work — eliminates almost all unpaid extras.
What's the easiest way to track if my estimates are accurate?
+
Compare what you quoted against what the job actually cost, every time. The easiest way is software that does it automatically: TradeShield's Insights tab shows quoted vs. actual once you mark a job complete, so you don't need to maintain a spreadsheet.
Should I raise my prices if I keep underbidding?
+
Maybe — but first find out why you're underbidding. If it's a markup-vs-margin math error or optimistic labor estimates, fixing the estimate is more precise than a blanket price increase. Track estimated vs. actual for a few jobs, find the pattern, then adjust your rates or your assumptions accordingly.