I have ID numbers with the date of purchase:   ID Number           Purchase Date and Time 1234                     01OCT2008:10:00:13 1234                      09SEP2009:16:00:23 1234                     14MAY2012:10:00:27 567                        07JAN2009:16:00:20 789                              .... 789 234 234 234   And so on and so forth. I want to loop through the purchase date and time by ID numbers and count the number of days between the purchase date. So basically I want to ask " How many days ago did the same person make that purchase. So I want a count of days between first record and second, then the second and third for each ID number.   My code isn't that great now,   DATA COUNTS1; SET SUMMARY; BY ID_NUMBER;   FIRST_DATE= DATEPART(FIRST.PURCHASE_DATE); END_DATE = DATEPART(LAST.PURCHASE_DATE); DO I= FIRST_DATE TO END_DATE; DAYS= INTCK('DAYS',FIRST_DATE,END_DATE); OUTPUT; END; PUT DAYS; RUN;   New to SAS, so please help me out.  ... View more