Its a Collection of custom Salesforce Formulas, feel free to contribute by adding new ones
DATE(IF((MONTH(DATEVALUE(CreatedDate)) + 1) = 13, YEAR( DATEVALUE(CreatedDate) ) +2, YEAR( DATEVALUE(CreatedDate) ) +1), IF((MONTH(DATEVALUE(CreatedDate)) + 1) = 13, 1, MONTH(DATEVALUE(CreatedDate)) + 1), 1) - 1
Result: IF CreatedDate = 15/12/2016 THEN Your_Custom_Field__c = 31/12/2017
Formula: Returns the number of business days between two dates (Week_Start_Date__c and Week_End_Date__c)
CASE(MOD( Week_Start_Date__c - DATE(1985,6,24),7),
0 , CASE( MOD( Week_End_Date__c - Week_Start_Date__c ,7),1,2,2,3,3,4,4,5,5,5,6,5,1),
1 , CASE( MOD( Week_End_Date__c - Week_Start_Date__c ,7),1,2,2,3,3,4,4,4,5,4,6,5,1),
2 , CASE( MOD( Week_End_Date__c - Week_Start_Date__c ,7),1,2,2,3,3,3,4,3,5,4,6,5,1),
3 , CASE( MOD( Week_End_Date__c - Week_Start_Date__c ,7),1,2,2,2,3,2,4,3,5,4,6,5,1),
4 , CASE( MOD( Week_End_Date__c - Week_Start_Date__c ,7),1,1,2,1,3,2,4,3,5,4,6,5,1),
5 , CASE( MOD( Week_End_Date__c - Week_Start_Date__c ,7),1,0,2,1,3,2,4,3,5,4,6,5,0),
6 , CASE( MOD( Week_End_Date__c - Week_Start_Date__c ,7),1,1,2,2,3,3,4,4,5,5,6,5,0),
999)
(FLOOR(( Week_End_Date__c - Week_Start_Date__c )/7)*5)
Result: IF Week_Start_Date__c = 18/09/2016 AND Week_End_Date__c = 26/09/2016 THEN Your_Custom_Field__c = 6
IF( NOT( ISBLANK( Date_Of_Birth__c) ) ,
IF( DATE( 2000 , MONTH( Date_Of_Birth__c) , DAY( Date_Of_Birth__c) ) <= DATE( 2000 , MONTH( TODAY() ) , DAY( TODAY() ) ),
YEAR (Today()) - YEAR ( Date_Of_Birth__c),
YEAR (Today()) - YEAR ( Date_Of_Birth__c) -1 ),
0)
Result: Date_Of_Birth__c = 01/01/1980 and Today = 07/10/2016
IF Day and Month Date_Of_Birth__c <= Day and Month TODAY()
THEN YEAR (Today()) - YEAR ( Date_Of_Birth__c) = 36
ELSE YEAR (Today()) - YEAR ( Date_Of_Birth__c) -1 = 35