Hello,
It is defined by the setting of Planning type Transaction MC8B (Planning type: Change) future periods.
Go to MC8B with Planning type SOPKAPA for product group andSOPKAPAM for individual material press enter
after that go to header menu Goto---Planning type Info ( CRTSHIFF12) here define the Planning start and Future period in planning Horizon and save it.
After that check in MC81 and MC87.
Best Regards,
R.Brahmankar