PV Function

PV.js

// Copyright (c) 2012 Sutoiku, Inc. (MIT License)

function PV(rate, periods, payment, future, type) {
  // Initialize type
  var type = (typeof type === 'undefined') ? 0 : type;

  // Evaluate rate and periods (TODO: replace with secure expression evaluator)
  rate = eval(rate);
  periods = eval(periods);

  // Return present value
  if (rate === 0) {
    return - payment * periods - future;
  } else {
    return (((1 - Math.pow(1 + rate, periods)) / rate) * payment * (1 +rate * type) - future) / Math.pow(1 + rate, periods);
  }
}