Hi @SASUser0001,   You can use the implied loop of the DATA step instead of an explicit DO loop: data have; input date :date. A :percent. B; format date date11. A percent7.2; cards; 30-Sep-01 0.45% 3500 31-Dec-02 1.02% 2000 31-Mar-04 0.58% 4800 30-Jun-05 0.93% 5698 30-Sep-06 0.74% 5896 ; data want; set have; retain new_index 62799.435; output; if _n_=1 then new_index=b; new_index=new_index/(1+a); format new_index best11.; run; ... View more

@SASUser0001 wrote: hi this is my programe where should I use   macro d1(name, list) proc summary data=total nway missing 　 var &list output out= data1 (drop=_type_ _freq_) sum=   run mend d1     Please help us all out and don't post code that doesn't have semi-colons and doesn't have % signs on the macro commands and has other obvious syntax errors. Please use the "running man" icon and post your code in the window that appears.   Also, @ballardw has already explained that you need to do the multiplication in a data step after your PROC SUMMARY, and he has given example code. Give that a try. ... View more

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You probably want to add an OUTPUT statement to your loop.   https://documentation.sas.com/?docsetId=lestmtsref&docsetTarget=n1lltvbis7ye1an1eryo4leh2mck.htm&docsetVersion=9.4&locale=en   do i = 1 to 6; balance=total_balance; interest+(((balance*rate)/100)/365)*30; bal_1=balance+Interest; output; end; If you want multiple variables with the different months you may want an array instead.   Here's a tutorial on using Arrays in SAS https://stats.idre.ucla.edu/sas/seminars/sas-arrays/   @SASUser0001 wrote: hi I am looking to calculate interest for 6 months. where interest is compounded monthly. I have try to use do loop something like this but it doesnt calculate for 6 months. it only give me interest for first month. help please.    do i = 1 to 6; balance=total_balance; interest+(((balance*rate)/100)/365)*30; bal_1=balance+Interest; end;   ... View more