A method for dynamically freeing storage space in a tiered storage system includes reading attribute values associated with data sets residing on a first storage tier. The method compares characteristics of the data sets to the attribute values to determine which initial data sets qualify to be moved from the first storage tier to a second storage tier. The method further determines whether movement of the initial data sets creates a desired amount of free space on the first storage tier. In the event the movement does not create the desired amount of free space, the method modifies the attribute values, determines which additional data sets qualify to be moved from the first storage tier to the second storage tier, and recalculates the amount of free space that would be generated. A corresponding system and computer program product are also disclosed.