Calculates your Ontario income tax from a semi-monthly paycheque.

OntarioTaxCalculator.js

function taxFromSemiMonthlyPaycheque(paychequeAmt) {
  var annualized = paychequeAmt * 24;
  
  var annualTax = ontarioTax(annualized) + federalTax(annualized);
  
  return annualTax / 24;
};

  /*
   * 5.05% on the first $42,201 of taxable income, +
   * 9.15% on the next $42,203, +
   * 11.16% on the next $65,596, +
   * 12.16% on the next $70,000, +
   * 13.16 % on the amount over $220,000
   */
var ontarioBrackets = [
  {size: 42201, rate: .0505},
  {size: 42203, rate: .0915},
  {size: 65596, rate: .1116},
  {size: 70000, rate: .1216},
  {size: 9999999999, rate: .1316}
];

/*
 * 15% on the first $45,916 of taxable income, +
 * 20.5% on the next $45,915 of taxable income (on the portion of taxable income over $45,916 up to $91,831), +
 * 26% on the next $50,522 of taxable income (on the portion of taxable income over $91,831 up to $142,353), +
 * 29% on the next $60,447 of taxable income (on the portion of taxable income over $142,353 up to $202,800), +
 * 33% of taxable income over $202,800.
 */
var federalBrackets = [
  {size: 45916, rate: .15},
  {size: 45915, rate: .205},
  {size: 50522, rate: .26},
  {size: 60447, rate: .29},
  {size: 9999999999, rate: .33}
];

function tax(annualIncome, brackets) {
  var totalTax = 0;
  var remainingIncome = annualIncome;
  
  for (var i=0; i<brackets.length; i++) {
    var bracket = brackets[i];
    if (remainingIncome <= bracket.size) {
      return totalTax + remainingIncome * bracket.rate;
      
    } else {
      var bracketMaxTax = bracket.size * bracket.rate;
      totalTax += bracketMaxTax;
      remainingIncome -= bracket.size;
    }
    
  };
  
  throw {};
}

function ontarioTax(annualIncome) {
  return tax(annualIncome, ontarioBrackets);
}

function federalTax(annualIncome) {
  return tax(annualIncome, federalBrackets);
}

function testTax() {
  var result = taxFromSemiMonthlyPaycheque(5000);
  
  console.log(result)
}