IsGrounded Script Not Working

My IsGrounded Script Is Not Working And I Cant Figure Out Why.

      public void UpdateStats()
 {
      if (IsGrounded == true)
      {
           HitDistance = 0.35f;
      }
      if (Physics.Raycast(transform.position - new Vector3(0, 0.85f, 0), -transform.up, HitDistance, IsGround))
      {
           IsGrounded = true;
      }
      else
      {
           IsGrounded = false;
      }
 }
      void Update()
      {
           UpdateStats();
      }