How Do You Build an Estimate From Sub Bids?

On a commercial job the general contractor buys most of the work from subcontractors, so most of its estimate is their prices. The estimator's job on bid day is assembly: deciding which number carries for each trade, adding the work the GC performs itself and the cost of running the job, and applying markups.

Do not wait for the bids to start. Price each trade first from your own takeoff and history, as public owners do with their own estimates: federal agencies prepare an independent estimate "in as much detail as though the Government were competing for award" (FAR 36.203), and the Federal Highway Administration calls the engineer's estimate "the benchmark for analyzing bids" (FHWA). Your plug is that benchmark: it tells you whether a bid is high, low or missing scope.

1. Plug every division. Write your own number for each trade package from quantities and unit costs or recent bids on similar work. Keep it as its own line, marked as a plug.
2. Price your own work separately: self-performed labor, material and equipment, and allowances. These lines always count.
3. Level each package's bids against one scope, so each bidder's number covers the same work. See how to level subcontractor bids.
4. Choose what carries: the awarded bid if there is one; otherwise the bidder you intend to use; otherwise the lowest leveled bid. With no bids in, the plug carries.
5. Replace the plug, not the division. The carried bid takes the plug's place; your own lines in that division stay.
6. Add general conditions: supervision, temporary facilities, site services, equipment, insurance and permits that are not in any sub's scope. See what general conditions are.
7. Apply markups in a stated order: contingency on cost, then fee on cost plus contingency, plus any bond, insurance or tax your contract requires.
8. Save the version you submit and do not change it. If a bid moves after you submit, that is a new version.

The job is fictional: "Bramble Creek Dental", a 6,000-square-foot clinic fit-out. The GC self-performs rough carpentry and buys four trades. Bids are in on three; HVAC bids are not.

General conditions add up as $40,000 + $4,500 + $4,800 + $2,700 = $52,000. Across the three divisions with bids, the bids came in $450 under the plugs (−$6,600 + $2,900 + $3,250). The HVAC plug is the open risk: it is $92,000 of the bid with no sub's price behind it yet, so it is the first thing to chase before the bid goes out.

• Carrying a base bid instead of the leveled bid, so excluded scope is missing from your estimate.
• Replacing the whole division with the bid, and losing your own self-performed lines in it.
• Keeping the plug and adding the bid, and counting the trade twice.
• Putting general conditions items a sub already carries (temporary power, cleanup) in both places.
• Applying fee before contingency without meaning to, or changing the order between versions.
• Changing a submitted number in place, so nobody can say later what the bid was.

When the job is won, the same carried numbers become the budget each award is measured against, and later the schedule of values each sub bills from.

Conflo's Estimate is organized by CSI division. Each line is a plug, labor, material, equipment, subcontract or allowance line with a quantity, unit and unit cost. When a trade bid for a division has a price, it replaces that division's plug lines only: the awarded bid first, then the bid you selected in leveling, then the lowest leveled bid. You can also choose a specific bidder for the estimate or keep your plug. Each division shows the carried bid against your plug.

General conditions have their own tab, as quantity × rate rows grouped by category, and markups such as contingency, insurance, bond, fee and tax are applied in the order you set. Freeze for bid keeps a copy of the version that cannot change, and the Client Proposal reads its numbers from that frozen version. The estimate is visible only to the general contractor.

An estimate built from sub bids is only as good as the plugs under it and the leveling before it. Plug every trade first, carry leveled numbers, replace only the plug, and apply markups the same way every time.

Then freeze what you submit. When the owner asks what the bid was, or a sub's number moves the next morning, you will have the answer.

See how the estimate works in Conflo

1. FAR 36.203, Government estimate of construction costs — Acquisition.gov, U.S. General Services Administration. Read October 16, 2026.
2. Guidelines on Preparing Engineer's Estimate, Bid Reviews and Evaluation (October 7, 2021), Preparing Engineer's Estimate — Federal Highway Administration. Read October 17, 2026.