Nobody sets out to lose money on a bid. But it happens all the time — not because GCs are bad at math, but because the bidding process has a dozen places where small oversights turn into big losses.
After analyzing thousands of construction bids, these are the 13 mistakes that show up most often. Some are obvious in hindsight. Others are subtle enough that you might be making them right now.
1. Comparing Bids by Bottom-Line Price Only
This is the most common and most expensive mistake. Two bids can show the same total and include completely different scope. The $45,000 HVAC bid that excludes the thermostat, ductwork modifications, and permit fees is not cheaper than the $52,000 bid that includes everything.
Fix
Always compare at the line-item level. Break every bid into the same categories and verify scope alignment before comparing price.
2. Not Reading the Exclusions
Exclusions are where bidders hide the change orders. "Excludes unforeseen conditions" sounds reasonable until you realize it means the sub isn't responsible for anything they didn't see coming. Which is everything underground, behind walls, or above ceilings.
Fix
Read exclusions first. They tell you more about a bid's true cost than the included items do.
3. Accepting Lump Sum Bids Without Breakdown
A lump sum with no line items is a black box. You can't verify quantities, you can't compare scope, and you have no leverage when negotiating change orders. If the sub won't break it down, they're either hiding something or haven't done the detailed takeoff.
Fix
Require itemized breakdowns from every bidder. Make it part of your bid invitation template.
4. Ignoring Unrealistically Low Bids
A bid that's 30% below the others is a problem, not a bargain. The sub either made a math error, excluded significant scope, or is planning to make it up in change orders. Awarding to a drastically low bidder almost always costs more in the end.
Fix
If a bid is 20%+ below the average, require a detailed explanation before considering it.
5. Not Verifying Quantities Against the Takeoff
Bidders make quantity mistakes. A flooring sub might measure 1,800 SF when your takeoff shows 2,100 SF. If you don't catch it before signing, you're paying for the difference as a change order — at a premium rate.
Fix
Spot-check quantities on the top 5-10 line items of every bid against your own takeoff numbers.
6. Bid Shopping
Sharing one sub's price with another to drive them lower destroys trust and your reputation. Word gets around fast in the trades. The subs who hear about it will either stop bidding your work or start padding their numbers.
Fix
Keep bid pricing confidential. If you want better numbers, provide clearer scope documents and give bidders more time.
7. Rushing the Bid Window
Giving subs 48 hours to bid a complex project guarantees sloppy estimates. They won't have time for a detailed takeoff, so they'll pad their numbers or exclude anything they're unsure about. Either way, you get worse bids.
Fix
Allow a minimum of 5-7 business days for standard scopes, 10-14 days for complex ones.
Stop making these mistakes manually
EstimateHawk automates the tedious parts of bid evaluation — extraction, normalization, and scope gap detection — so you catch problems before they cost you.
Run your first comparison — $498. Vague or Incomplete Bid Invitations
If your bid invitation doesn't clearly define the scope, don't be surprised when every bid defines it differently. "Bid the kitchen renovation" is not a scope document. Without specific drawings, specifications, and scope narratives, every bidder is guessing — and they're all guessing differently.
Fix
Include drawings, specifications, a scope narrative, and a list of specific inclusions/exclusions in every bid package.
9. Skipping Reference Checks
A good price from a sub you've never worked with is just a number on paper. Without references, you don't know if they finish on time, manage change orders fairly, or clean up after themselves. The 10 minutes it takes to call two references can save you weeks of headaches.
Fix
Require two project references from any new bidder. Call them and ask about timeline, quality, and change order behavior.
10. Not Accounting for Mobilization and General Conditions
Temporary toilets, dumpsters, site fencing, temporary power — these costs add up fast. If they're not explicitly included in the bid, they're going to show up as an extra. And they're rarely cheap.
Fix
Include a general conditions line in your bid comparison. If a bidder excludes them, add a realistic estimate to their total.
11. Forgetting About Warranty Terms
A one-year workmanship warranty and a five-year warranty are not the same thing, even if the bid price is identical. Factor in the cost of potential callbacks and repairs when comparing bids with different warranty terms.
Fix
Standardize warranty requirements in your bid invitations. Minimum two years on workmanship, manufacturer warranties on materials.
12. Awarding Before the Budget Is Finalized
Committing to a sub before the owner has approved the budget creates pressure to make the numbers work after the fact. If the budget gets cut, you're either renegotiating (which damages the relationship) or eating the difference.
Fix
Don't issue subcontracts until the project budget is owner-approved. Use letters of intent with clear scope and pricing if you need to hold a sub's commitment.
13. Not Documenting the Bid Leveling Process
If you don't document why you chose a particular bidder, you can't defend that decision later. When the owner asks why you went with Bidder B instead of the cheapest option, "they felt like the best fit" isn't going to cut it.
Fix
Keep your bid comparison matrix and a brief written rationale for every award. It takes 5 minutes and can save you hours of difficult conversations later.
The Common Thread
Every one of these mistakes comes from the same root cause: not having a systematic process for evaluating bids. When you're moving fast — and every GC is always moving fast — the details get missed.
The fix is a repeatable system. Whether that's a spreadsheet template, a checklist, or a tool like EstimateHawk that automates the comparison, the point is to make bid evaluation consistent so the same mistakes don't keep costing you money.