Evaluates the cumulative interest paid between two periods.

rate—Interest rate.

n_periods—Total number of payment periods. n_periods cannot be less than or equal to 0.

present_value—The current value of a stream of future payments, after discounting the payments using some interest rate.

start—Starting period in the calculation. start cannot be less than 1; or greater than end_per.

end_per—Ending period in the calculation.

when—Time in each period when the payment is made, either 0 for at the end of period or 1 for at the beginning of period.

result—The cumulative interest paid between the first period and the last period. If no result can be computed, NaN is returned.

Double—If present and nonzero, double precision is used.

Function CUM_INTR evaluates the cumulative interest paid between the first period and the last period.

It is computed using the following:

where interesti is computed from the function INT_PAYMENT for the ith period.

In this example, CUM_INTR computes the total interest paid for the first year of a 30-year $200,000 loan with an annual interest rate of 7.25%. The payment is made at the end of each month.

PRINT, CUM_INTR(0.0725 / 12, 12*30, 200000., 1, 12, 0)

; PV-WAVE prints: -14436.5