DURATION OF STAY………DAYS indicates the number of days you may stay in the Schengen area. The days should be counted from the date you enter the Schengen area (the entry stamp) to the date you exit the Schengen area (the exit stamp), i.e. both days included.
The period of time between "FROM …UNTIL" is usually longer than the number of days printed in the "DURATION OF STAY" field. The difference in period is meant to give you flexibility to plan your entry into and exit from the Schengen area, but your stay in the Schengen area must never exceed the exact number of days in the "DURATION OF STAY …DAYS" field. No matter how many days you have stayed in the Schengen area, you must leave no later than the date printed in the "UNTIL" field."