990-PF is usually filed by private foundations, and some of these foundations may have to pay an excise tax. Form 990-PF is used to calculate the amount of excise tax that has to 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 assets of the foundation other than those used or withheld for exempt purposes. The distributable amount that can be determined from the minimum investment return is also calculated on the Form 990-PF.