A top-down estimate is an estimate based on past projects to predict the current cost and/or duration of the current project. It is also called an analogous estimate, as it involves using data from previous, similar projects to estimate activity durations1. Top-down estimates are usually done at the early stages of a project, when there is not enough detail or information available to perform more accurate estimates. They are useful for providing a rough order of magnitude (ROM) or a ballpark figure for the project scope, cost and schedule. Top-down estimates are typically faster and cheaper to produce than bottom-up estimates, but they are also less accurate and reliable23. References: 2: Project Cost Estimation: How to Estimate Project Cost - ProjectManager2 3: 11 Cost Estimating Methods (With Formulas and Examples) | Indeed.com3 1: Understanding the Analogous Estimating Technique | Runn1