CUMPRINC Function

CUMPRINC.js

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

// Some algorithms have been ported from Apache OpenOffice:

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function CUMPRINC(rate, periods, value, start, end, type) {
  // Credits: algorithm inspired by Apache OpenOffice
  // Credits: Hannes Stiebitzhofer for the translations of function and variable names
  // Requires getFutureValue() and getPartialPayment() from Formula.js [http://stoic.com/formula/]

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

  // Return error if either rate, periods, or value are lower than or equal to zero
  if (rate <= 0 || periods <= 0 || value <= 0) return '#NUM!';

  // Return error if start < 1, end < 1, or start > end
  if (start < 1 || end < 1 || start > end) return '#NUM!';

  // Return error if type is neither 0 nor 1
  if (type !== 0 && type !== 1) return '#NUM!';

  // Compute cumulative principal
  var payment = getPartialPayment(rate, periods, value, 0, type);
  var principal = 0;
  if(start === 1) {
    if(type === 0) {
      principal = payment + value * rate;
    } else {
      principal = payment;
    }
    start++;
  }
  for (var i = start; i <= end; i++) {
    if(type > 0) {
      principal += payment - (getFutureValue(rate, i - 2, payment, value, 1) - payment) * rate;
    } else {
      principal += payment - getFutureValue(rate, i - 1, payment, value, 0) * rate;
    }
  }

  // Return cumulative principal
  return principal;
}

Thank You so much sir! saved me so much time!