Top-down vs bottom-up estimations

Abstract

When starting a new project, an important task for the project manager, is the estimation process. This can both be an estimation regarding cost and time-frames. It is important to get the project off to a good start, given that success of the project depends on the estimation - both in regards to time and cost. When estimating (or in other words 'predicting the future'), the project manager can use the following methods:

- Top-down approach

- Bottom-up approach

By choosing the top-down approach, the project manager chooses to make an overall scope of the project. From here, the major elements of the project is being listed and estimated separately. This approach creates a rough idea of the project size and the different timeframes of the project elements. The advantages of using the top-down approach is less time consuming and requires a limited amount effort. The estimates created by this method often turns out larger than the ones, which has been found using the bottom-up approach.
The bottom-up approach is on the other hand a very time-consuming and costly method, but it gives a more accurate estimate of the project time and cost. By using the bottom-up approach, the cost and time frame is being calculated for every activity related to the project. The values and time frames are then aggregated in order to estimate the total cost and project time. The bottom-up approach is often used in order to gain stakeholders to buy in on the project.

Big idea

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References to use for later

Web: https://www.apm.org.uk/blog/three-ways-to-approach-cost-estimation/
Web: https://www.pmi.org/learning/library/top-down-bottom-up-pm-8496
Video: https://study.com/academy/lesson/top-down-bottom-up-estimating-techniques-in-project-management.html