Bottom-up estimating is a project management technique where individual tasks are estimated in detail before aggregating them to form a total project estimate. This method involves breaking down a project into smaller components, allowing for more accurate assessments of time, costs, and resources needed for each task. By focusing on the specifics of each task, teams can identify potential challenges and allocate resources more effectively. This approach contrasts with top-down estimating, where the overall project cost is determined first and then divided among tasks. Bottom-up estimating is often used in conjunction with project management methodologies like Agile or Waterfall.