A system and method for balancing instruction loads between multiple execution units are disclosed. One or more execution units may be represented by a slot configured to accept instructions on behalf of the execution unit(s). A decode unit may assign instructions to a particular slot for subsequent scheduling for execution. Slot assignments may be made based on an instruction's type and/or on a history of previous slot assignments. A cumulative slot assignment history may be maintained in a bias counter, the value of which reflects the bias of previous slot assignments. Slot assignments may be determined based on the value of the bias counter, in order to balance the instruction load across all slots, and all execution units. The bias counter may reflect slot assignments made only within a desired historical window. A separate data structure may store data reflecting the actual slot assignments made during the desired historical window.