You must enter periods on a supplier agreement to define the time period for the supplier agreement's validity. The supplier agreement will not be used if there is no valid period. You also must enter a maximum amount for the specified period. The consequence when the maximum amount is reached depends on the choice in the Maximum Amount Option field in the General tab. If no end date is specified, the supplier agreement has no defined valid until date.
You can have several periods during the lifetime of a supplier agreement. Periods cannot overlap, but they can have gaps. A period cannot be removed if there have been any purchases (using the supplier agreement) during it. The cumulative amount of all purchases made during a period are saved, specified for each period in the Periods tab. You can also see how many purchase order lines have been entered for each period.