PMT Function

PMT.js

// Copyright (c) 2012 Sutoiku, Inc. (MIT License)
 
// Some algorithms have been ported from Apache OpenOffice:
 
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function PMT(rate, periods, present, future, type) {
  // Credits: algorithm inspired by Apache OpenOffice

  // Initialize type
  var type = (typeof type === 'undefined') ? 0 : type;

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

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

Thanks for your beautifull code