There's a saying in construction: "The low bidder is the one who forgot to include something." It's a joke, but it's also true more often than anyone would like to admit.
Underbidding is one of the most persistent problems in the construction industry. Subs do it, GCs do it, and the end result is always the same — someone loses money. The question is who, and how much.
The Five Reasons Contractors Underbid
1. Honest Math Errors
Quantity takeoff mistakes, formula errors in spreadsheets, missed items on the plans. It happens. A sub doing a manual takeoff at 11 PM is going to miss things. The larger and more complex the project, the more opportunities for errors.
2. Incomplete Scope Understanding
The sub read the drawings but not the specifications. Or they priced the base scope but missed the alternates. Or they assumed standard conditions and didn't account for the 12-foot ceilings, the limited access, or the occupied building. They're not being dishonest — they just didn't understand the full scope.
3. Desperation for Work
When work is slow, contractors lower their margins to keep their crews busy. The logic makes sense in the short term — even a break-even job keeps the lights on. But it creates a cycle where the sub needs change orders just to survive the project.
4. Strategic Underbidding
Some contractors deliberately bid low to win the job, planning to recover their margin through change orders. They know the GC will pick the lowest price. They also know that once they're mobilized on site, the GC has limited leverage to push back on extras.
5. Market Pressure
When material costs are volatile, bidders face a choice: price at today's costs and risk being too high if prices drop, or price aggressively and hope costs don't rise. In competitive markets, the pressure to bid low pushes contractors to take risks they shouldn't.
How Underbidding Costs the GC
Catch underbidding before it costs you
EstimateHawk flags bids with missing scope, artificially low pricing, and items that other contractors included but this one left out.
Run your first comparison — $49When a sub underbids, the GC absorbs most of the consequences.
- Change orders — The most direct cost. Every item the sub underpriced or excluded becomes a change order at premium markup rates.
- Schedule delays — An underbidding sub often has cash flow problems. They can't buy materials on time, can't staff the job properly, and fall behind schedule.
- Quality shortcuts — When margins evaporate, corners get cut. Cheaper materials, fewer workers, less supervision. You might not notice until the warranty calls start.
- Relationship damage — Constant change order negotiations poison the working relationship. The sub resents losing money; the GC resents being nickeled and dimed. Nobody does their best work in that environment.
How to Protect Yourself
Know Your Market Rates
If you don't know what things should cost in your market, you can't identify a bid that's too low. Track your actual project costs over time. Build a database of what you've paid for common scopes. When a bid comes in 25% below your baseline, that's a red flag, not a bargain.
Require Itemized Breakdowns
Lump sum bids hide underbidding. When you can see the unit prices and quantities, you can spot the math errors and the unrealistic assumptions. A sub who quotes $3/SF for tile installation when the market rate is $6/SF either made a mistake or is planning to surprise you later.
Ask the Hard Question
When a bid looks too good, call the sub and ask directly: "Your bid is significantly below the other submissions. Can you walk me through your pricing?" A legitimate low bidder will have clear reasons — volume discounts, lower overhead, faster methods. A strategic underbidder will get vague.
Use Technology to Compare
Manual bid comparison takes hours, which means it often doesn't get done thoroughly. Tools like EstimateHawk extract line items from PDF bids, normalize the pricing, and flag outliers automatically — making it practical to do a detailed comparison on every project, not just the big ones.
The Bottom Line
Underbidding persists because the construction industry rewards the lowest price. The way to break the cycle is to evaluate bids on value, not just cost — and to have enough information to tell the difference between a genuinely competitive bid and one that's going to cost you more in the long run.