[net.invest] Need Equation for Interest Paid so far

rs173@hou2e.UUCP (R.SILVER) (10/23/85)

   I am writing a spreadsheet program to calculate return on
investment properties. 

   Can anyone give me an equation which gives i
the interest-paid to-date on a current loan with monthly-payments ?

   Thank you for any help.          Ron Silver   ...hou2e!ron7300!rs173