Progress Percentage by using late dates

Dear Friends 

Suppose you have an activity A .

whose early dates are 

Early Start  1 Apr 11 

Early Finish  30 Apr11

Whose Late Dates area 

Late Start 25 April 11

Late Finish 10 May 11

Now we are at 1 may , as per ealry dates your  planned progress must be 100 % while the  activity is 90% complete. This shows that it is delayed , now we want to use float then how to calculate planned progress  ?  so as not to show that we are delayed 

Thankyou 

Umer Mehmood