Posted on 08/02/2006
Ok, here's how you should calculate it.
function PMT (ir, np, pv, fv ) {
/*
ir - interest rate per month
np - number of periods (months)
pv - present value
fv - future value (residual value)
*/
pmt = ( ir * ( pv * Math.pow ( (ir+1), np ) + fv ) ) / ( ( ir + 1 ) * ( Math.pow ( (ir+1), np) -1 ) );
return pmt;
}
Let's buy a car priced at 10000$ with 30% advance, 20% residual value and 8% interest rate in 24 months.
present_value = 10000;
interest_rate = 8/100 / 12; // per month
number_periods = 24;
advance = present_value*30/100;
financed = present_value - advance;
residual_value = present_value*20/100;
rate = PMT ( interest_rate, number_periods, financed, residual_value );



















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