diff --git a/sys/kern/sched_ule.c b/sys/kern/sched_ule.c
index 708478f27558..25c827a0ac51 100644
--- a/sys/kern/sched_ule.c
+++ b/sys/kern/sched_ule.c
@@ -1450,6 +1450,21 @@ sched_initticks(void *dummy)
  * a [0, 100] integer.  This is the voluntary sleep time of a process, which
  * differs from the cpu usage because it does not account for time spent
  * waiting on a run-queue.  Would be prettier if we had floating point.
+ *
+ * When a thread's sleep time is greater than its run time the
+ * calculation is:
+ *
+ *                           scaling factor 
+ * interactivity score =  ---------------------
+ *                        sleep time / run time
+ *
+ *
+ * When a thread's run time is greater than its sleep time the
+ * calculation is:
+ *
+ *                           scaling factor 
+ * interactivity score =  ---------------------    + scaling factor
+ *                        run time / sleep time
  */
 static int
 sched_interact_score(struct thread *td)