# Talk:Documentation/Calc Functions/ISPMT

(1) Summary. Suggest the following alternative – “Calculates the interest paid in a period for an amortized loan, with a fixed payment each period”.
(2) Returns. Clarify that the currency unit is that used to specify Invest.
(3) Arguments, Rate. Presumably, you can enter a percentage or a decimal fraction?
(4) Period. Change “number of installments for calculation of interest” to “period for which interest is to be calculated”.
(5) Arguments, Total Periods. Change “installment” to “payment”.
(6) Arguments, Invest. Change “investment” to “loan”.
(7) Arguments, 1st bullet. “argument” should be plural. Insert space before open round bracket. Change “an” to “a”.
(8) Additional details. The following text from the Open Office page might be useful – “ISPMT considers a fixed rate loan, where you repay the same amount of capital at the start of each period, and pay interest on the outstanding balance at the end of each period. The interest you pay will depend on the remaining outstanding balance each period and will decline with time. ISPMT returns that interest. This is not the same as IPMT, where the total sum you pay each period (interest plus capital) is constant.”.
(9) Additional details. The formula used in the code appears to be ( Invest * Rate * (Period / Total Periods- 1.0) ). Please include this, nicely formatted.