When to use the right Estimate ?

q171 Between ROM, Budgetary and Definitive, when to use them ?

Let's say the question have no context just that, We are in planning, what estimate would you take


I toght that.....

Initiating or before = ROM

Planning = Budgetary

Executing ( close to the end ) = Budgetary



akbar.azwir's picture

ROM, a ballpark estimation of how much is the cost to complete the project. The level of detail is small. The variance is really high, can be up to 100% variance.

Budgetary, a more detailed estimation. Using a top down approach, usually using an analogous or parametric estimating. The variance is way less than ROM.

Definitive, a more detailed estimation that uses a bottom up approach. This is something that you can achieve after you have your WBS. The variance is less than Budgetary.


ROM -> Initiating

Budgetary -> Planning (early stage)

Definitive -> Planning (progressive elaboration)