If your planning must allow for regular periodic fluctuations, you can define custom distribution keys. The R/3 System distributes the total value you entered in planning to the individual periods, based on the distribution defined in the key.
You can create distribution keys before or during planning. SAP recommends creating them before planning begins if you know that organization-specific distribution keys are required.
Examples for distribution keys are seasonal fluctuations or shift schedules.
To define individual distribution keys, see the Implementation Guide (IMG) for the relevant Controlling component, under Planning® Manual Planning, for example under Maintain User-Defined Distribution Keys for cost centers.