Carrying Out the Total Forecast in Background Mode 
To start the total forecast in background mode,
from the menu screen of the forecast, select Forecast ® Total forecast ® Execute (background).The initial screen for Background Request appears.
Here, you can either start the forecast run immediately or you can plan it to start at a later date by means of a selection variant. The forecast is then carried out in background mode. More detailed information on background request procedures can be found in the SAP document ABAP/4: Generating and Printing Reports.

A repeat forecast (that is, the forecast is carried out again for a certain period) is not possible for the total forecast either in online or in background mode.