Why LoadLevelAsync dont give me progress, it is alwasys 0 ?

I wrote a simple script with startcoroutine() to load my level but when i run it, the async.progress always 0 every time i try, any help although it still take a long while for the level to load using UnityEngine; using System.Collections;

 public class StartButton : MonoBehaviour
 {
     public GameObject start;
     private int percent;
     public string level;
     public GameObject Text;
     public GameObject Bg;
     private AsyncOperation async;
     // Update is called once per frame
     void OnMouseUpAsButton ()
     {
         DestroyObject(start);
         Bg.SetActive (true);
         Text.SetActive (true);
         StartCoroutine (LevelLoader ());
          
     }   
     void Start()
     {
         Bg.SetActive (false);
         Text.SetActive (false);
     }
     private IEnumerator LevelLoader ()
     {
         async = Application.LoadLevelAsync (level);
         percent = (int)(async.progress*100);
         if (!async.isDone)
         {
             Debug.Log(percent);
             yield return null;
         }
 
     }
 
 }