Please try,
data have;
input customer$ product$ purchase_date : mmddyy10. days_supply;
format purchase_date mmddyy10.;
cards;
a R1 10/11/13 30
a R2 10/11/13 30
b R1 02/15/13 30
b R2 03/15/13 30
b R3 04/15/13 60
;
run;
data want;
set have;
do possession_date= purchase_date to intnx('day',days_supply,purchase_date);
output;
end;
format possession_date mmddyy10.;
run;
Thanks,
Jagadish
Thanks,
Jag