Budget at completion BAC
it is simply the original project estimate (usually the estimation of BAC is done during the planning phase). It is part of the original plan cost where you estimate how much the whole project will cost. BAC is may be less, more, or equal to the Estimate at completion (EAC) since the last will be the final cost of the project when it is finished.
Example: A Tech startup Company assigned you to manage a software development project. The software is expected to cost $300,000 for the developers, $50,000 for the hosting servers, and $5,000 for testing.
BAC is the estimated value of what the project will cost.
BAC = $300,000 + $50,000 + $5,000, or $355,000.