Does anyone out there know the equation for Microsoft&#039;s IPMT function?<BR><BR>The IPMT function returns the interest payment for a given period of an annuity based on periodic, fixed payments and a fixed interest rate.<BR><BR>I&#039;ve found info on the PTM function ( but can&#039;t seem to figure out the equation for the IPMT function.<BR><BR>I&#039;d like to have this function to incorporate into an ASP-based spreadsheet I&#039;m writing.<BR><BR>Thanks,<BR>Chris<BR><BR>