Calculating Overhead 
When you save a unit cost estimate, overhead costs (overhead rates and/or process costs) are calculated automatically and inserted as items of category G (overhead rates) or X (process costs).
You can also calculate overhead rates and process costs manually, using the Calculate Overhead function.
Prerequisites
A costing sheet has been entered in the valuation variant.
An overhead key (if applicable) has been entered in the master data of the reference object, such as the material.
For base planning objects, the costing sheet and overhead key have been entered in the master data of the base planning object.
Procedure
Go to the list screen of the unit cost estimate.
Choose
Functions 
Calculate Overhead 
.
Result
Overhead rates and process costs are calculated based on the costing sheet and overhead key.
Items of category G (overhead rates) and X (process costs) are inserted.