What is the difference between a cost estimate, cost baseline, and project budget?

A cost estimate is the predicted cost of each activity or work package based on available information at a given time. The cost baseline is the approved, time-phased budget that serves as the reference point for measuring cost performance, including all authorized work and contingency reserves but excluding management reserves. The project budget equals the cost baseline plus management reserves. In formula terms: activity estimates plus contingency reserves equals cost baseline, and cost baseline plus management reserves equals project budget.