### Title

Loan Amortization Schedule

### Post

Hi,

I'm trying to build a Auto Loan Finance system and I'm working with Filemaker 11's PMT function successfully, however, I am building an amortization schedule to calculate balloon payments (eg. 60month term OVER 84 month amortization). I have a script that runs and generates the proper amount of records for each period or month and calculates the Interest, Cumulative Interest, Principle Balance, Payment Date, and Days Since Last Payment. What I've found is my system being out cents at the end of the loan and I believe this is because of some months being longer than others. I changed my calculations to calculate interest daily to compensate for this, however, I'm out a few dollars now.

It seems that when I was calculating it monthly it was closer to all the calculations that I was comparing to an online amortization schedule calculator. The first month's interest was out $.72 and every month here and there was out a penny.

I don't understand why? Am I missing something obvious?

I'm using the following data:

Principle Balance: 10500; Interest Rate:6%, Term & Amortization: 60 Months (keeping it simple before I get into balloon payments)

I've attached a copy of my script I'm working with. Note: The payment stays the same therefore I use 'Get Value from Previous Record'.

Welcome to the joys of "round off error".

When you compute values by dividing and/or by multiplying by percent values, The result is stored in fileMaker down to many decimal places after the cents place--just like punching it up on a calculator display, but your report likely displays the values rounded to the nearest cent. That small difference between the rounded and unrounded values can add up over the life of the loan to produce a small discrepancy. If you use the round function to round each calculation to the nearest cent, I think you'll see this discrepancy disappear.