What is calculated on Form 990-PF?

Private foundations usually file 990-PF, and some may have to pay an excise tax. Form 990-PF is used to calculate the amount of excise tax that has to be paid by a private foundation.
 
The form is also used to calculate the minimum investment return, which is 5% of the excess of the combined fair market value of all the foundation assets other than those used or withheld for exempt purposes. The distributable amount from the minimum investment return is also calculated on Form 990-PF.