number of Saturdays between those 2 dates. Create formula field
FLOOR(( End_Date__c - Start_Date__c )/7) + IF(OR (WEEKDAY(Start_Date__c )=7, WEEKDAY(End_Date__c )=7, WEEKDAY(Start_Date__c )>WEEKDAY(End_Date__c )),1,0) If you want the number of Sundays: FLOOR(( End_Date__c - Start_Date__c )/7) + IF(OR (WEEKDAY(Start_Date__c )=1, WEEKDAY(End_Date__c )=1, WEEKDAY(Start_Date__c )>WEEKDAY(End_Date__c )),1,0) This is easily changed for any day of the week. You only need to change the "WEEKDAY" number (1 for Sunday, 2 for Monday, 3 for Tuesday, etc) in this part: WEEKDAY(Start_Date__c )=1, WEEKDAY(End_Date__c )=1