> the format is not relevant Not too sure what this means.   %let end=2014/2;   Your test resolves to   if 2013 <= QUARTER <= 1007 which always fails.       ... View more

Something like this may work (not tested): data want; set have; array startdates startdate1-startdate20; array enddates enddate1-enddate20; enrolled=0; do _N_=1 to dim(startdates); /* find first enrollment within interval */ if '01jan2015'd<=enddates(_N_)<='31dec2017'd or '01jan2015'd<=startdates(_N_)<='31dec2017'd then do; enroll_from=max(startdates(_N_),'01jan2015'd); enroll_to=min(enddates(_N_),'31dec2017'd); enrolled=intck('month',enroll_from,enroll_to,'C')>=6; leave; end; end; do _N_=_N_+1 to dim(startdates) while(not enrolled); if startdates(_N_)>'31dec20017'd then leave; if startdates(_N_)-enroll_to>45 then enroll_from=startdates(_N_);     enroll_to=min(enddates(_N_),'31dec2017'd);    enrolled=intck('month',enroll_from,enroll_to,'C')>=6; end; drop enroll_from enroll_to; run; ... View more