The base bid is the starting point for contract pricing. It covers everything in the plans and specs that the builder and contractor agreed to during bidding, at the price stated in the contract. Any work not explicitly included in the base bid requires a change order and an upward adjustment to the contract price.
When a builder requests bids from multiple contractors, the base bid is the comparable number used to select the lowest bidder or the best value. To make base bids meaningful, the scope has to be clearly defined in the plans and specifications. Vague scopes lead to bids that don’t align because each bidder interprets what’s included differently. Alternates and allowances sit on top of the base bid: an alternate might be an upgrade appliance package, and an allowance covers items to be selected later. Tracking the base bid separately from change orders and alternates is essential for cost control. If a project’s contract price starts at a base bid of 400k and then accrues 50k in changes and allowance overages, the builder needs to see both numbers to understand the true cost.