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Estimating & Bidding

Additive Alternate

In Plain English

An optional add-on item priced separately so the owner can include it if budget allows.

Definition

An additive alternate is a scope item listed separately in a bid that the owner may add to the base bid contract. Bidders price it independently so the owner can decide whether to include it based on available budget. Additive alternates allow owners to expand project scope without re-bidding.

Why It Matters in Bidding

Additive alternates let owners stretch a budget and rank priorities without re-bidding, but they complicate the estimator's job because each alternate must be cleanly carved out and priced as standalone scope. The way alternates are accepted can also change which bidder wins, since award is often based on base bid plus selected alternates. Misallocating shared costs into an alternate can leave money on the table or distort competitiveness.

Example

On a school bid the base scope covers the building shell while Additive Alternate No. 2 prices a separate $180,000 site-paving package, letting the district award the shell now and add the paving only if bids come in under budget.

Related Terms

Deductive AlternateAlternatesBase BidBid Form

Frequently Asked Questions

An additive alternate prices work added on top of the base bid, so the contract grows if accepted. A deductive alternate prices work removed from the base bid, reducing the contract if selected. Owners use additive alternates when the base scope is the minimum acceptable project and added items depend on remaining budget after bids open.
Public solicitations typically state that the low bidder is determined by base bid plus the alternates the owner elects to accept, often in a predefined order. This means a contractor can win or lose based on alternate pricing, so estimators price them carefully and avoid hiding general costs that belong in the base bid.
Price it as discrete, self-contained scope with its own takeoff, subcontractor quotes, markup, and any added general conditions or mobilization the add-on triggers. Avoid double-counting costs already in the base bid, and clearly document inclusions and exclusions so the owner and bid form reflect exactly what acceptance buys.

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