trigger

gistfile1.txt

    public static Set<String> storedTargetIds = new Set<String>();
    
    public static void beforeInsert(List<Referral__c> newList){

        List<Target__c> targetsList = [SELECT Id,Start_Date__c,End_Date__c FROM Target__c];

        for (Referral__c r : newList){
          if (r.Date__c != null){
            Date referralDate = r.Date__c;
            for (Target__c target : targetsList){
              if (referralDate > target.Start_Date__c && referralDate <= target.End_Date__c){
                r.Target__c = target.Id;

                // after you find target, add Id to Set
                storedTargetIds.add(target.Id);

              }
            }
          } // closes outer if
        } // closes outer for

        System.debug(storedTargetIds);
    }
    
    
    public static void afterInsert(List<Referral__c> newList){

        Set<Target__c> updateSet = new Set<Target__c>();
        List<Target__c> tList = [SELECT Id,User__c,Start_Date__c,End_Date__c,Total_Referrals__c FROM Target__c];

        List<AggregateResult> arList = [SELECT count(Id) cnt, Target__c tgt FROM Referral__c WHERE Target__c IN :storedTargetIds GROUP BY Target__c];

        for (AggregateResult ar : arList){
        
        // no need for below line
          // if (ar.get('tgt') != null){
            Id targetId = (Id)ar.get('tgt');
            Target__c foundTarget=new Target__c(Id=targetId, Total_Referrals__c=(Decimal)ar.get('cnt'));

            for (Referral__c r : newList){
              if (targetId == r.Target__c){
                foundTarget.User__c = r.Referred_To__r.OwnerId;
              }
            }

            updateSet.add(foundTarget);
          // }
        }

        if (updateSet.size() > 0){
          List<Target__c> updateList = new List<Target__c>();
          updateList.addAll(updateSet);
          update updateList;
        }
    } // closes afterInsert