Calculate payments based on APR

[Robert T. Repko (R Squared Consultants)]

Believe it or not at 4/13/2009 08:23 PM, Kenneth Brody said:
>Robert T. Repko (R Squared Consultants) wrote:
>[...]
>>Is it possible to get a daily payment amount instead of monthly.  I 
>>can see the need to calculate a daily rate so when people make 
>>payments I can calculate the principal and interest for x number of 
>>days.  I tried substituting 365 in place of 12 but the numbers 
>>didn't come out right.
>
>In what way didn't they "come out right"?  If you make 365 payments 
>in one year, then you divide the yearly interest rate by 365 to get 
>the per-period interest rate, just as you would divide by 12 for 12 
>monthly payments.
>
>--
>Kenneth Brody

That's what I thought but when I ran it my answer was different by 
.315/month, 89.74 vs. 89.425

pa="12";' it will be the number of months (12, 24, 36, ...) input by 
data entry, but I'll use 12 in this example.

pi=pa*"30.42"="365";' since I have months I have to convert to 1 year

ep(8,.5)=(eo*"100")/"365" = .03808;'  eo is stated as .1390 so I 
multiply by 100 to convert to 13.9 for use in the tvm_pmt command.

ez="1000";' amount of loan

eh = TVM_PMT(pi,ep,ez,"0") = $2.94 daily payment

"2.94" * "365" / "12" = 89.425

2.94 is daily payment, mult. by 365 for annual payment, divide by 12 
for monthly payment = 89.425.  That's a difference of ~ 
$.315/month.  Maybe I'm wrong but I wouldn't expect that much 
difference between daily vs. monthly calculations, and I would expect 
the daily calculations to be higher than the monthly calculations not lower.