nureya
It is the Annual Estimate which is often the reason for all doubts of users in these performance based plans. Please study well the post here and correlate to your situation, which might answer your queries.: Behavior of Performance Based Plan in SAP PM.
If you are left with some more queries, please post your remaining or original query to Enterprise Resource Planning space which is best suited for this subject.
Good luck
KJogeswaraRao