ontario-tax-calculator.js

const INCOME = 100_000;

// ----- 2022 ----- //

// https://www.canada.ca/en/revenue-agency/services/forms-publications/payroll/t4032-payroll-deductions-tables/t4032on-jan/t4032on-january-general-information.html

const CPP_BRACKETS = [
  [   3_500, 0     ], // exemption
  [  61_400, 0.0570], // cap
  [Infinity, 0     ],
];
// Max contribution 3,499.80

const EI_BRACKETS = [
  [  60_300, 0.0158], // cap
  [Infinity, 0     ]
];
// Max contribution 952.74

const FEDERAL_TAX_BRACKETS = [
  // [MAX amount, % tax rate]
  [  14_398, 0    ],
  [  50_197, 0.15 ],
  [ 100_392, 0.205],
  [ 155_625, 0.26 ],
  [ 221_708, 0.29 ],
  [Infinity, 0.33 ],
];

const ON_TAX_BRACKETS = [
  [  46_226, 0.0505],
  [  92_454, 0.0915],
  [ 150_000, 0.1116],
  [ 220_000, 0.1216],
  [Infinity, 0.1316],
];

// Tax on top of tax
const ON_SURTAX_BRACKETS = [
  [   4_991, 0   ],
  [   6_387, 0.20],
  [Infinity, 0.56]
];


// ----- BRACKETS ----- //

// transform bracket caps into bracket increments that the bracket rate works on
// @return Array<[cap, rate]> => Array<[increment, rate]>
// Eg, [[10, 0.15], [20, 0.30]] => [[10, 0.15], [10, 0.30]];
function getBracketIncrements(brackets) {
  let lastCap = 0;
  return brackets.map(([cap, rate]) => {
    const bracket = [cap - lastCap, rate];
    lastCap = cap;
    return bracket;
  });
}

// @result Array<Tuple<rate, amount>>
function calcBracketBreakdown(brackets) {
  return (amount) => {
    let remainder = amount;
    const result = [];

    for (let [increment, rate] of getBracketIncrements(brackets)) {
      const incrementAmount = Math.min(increment, remainder);

      result.push([rate, incrementAmount * rate]);

      remainder -= increment;
      if (remainder <= 0) {
        break;
      }
    }

    return result;
  };
}

function calcBracketsTotal(bracketBreakdown) {
  return bracketBreakdown
    .map(([_, amount]) => amount)
    .reduce((sum, amount) => sum + amount, 0);
}


// ----- DISPLAY ----- //

// Adds comma separators, and 2 decimal places
function formatDollars(n) {
  return '$' + n.toFixed(2).replace(/\B(?=(\d{3})+(?!\d))/g, ",");
}

function formatPercent(p) {
  return (p * 100).toFixed(2) + '%';
}

function displayBracketBreakdown(bracketBreakdown, spacing = 2) {
  bracketBreakdown.forEach(([rate, amount]) => {
    const formattedAmount = `${formatDollars(amount)}`;
    const rateInPercent = `${formatPercent(rate)}`;
    if (amount) {
      console.log(`${' '.repeat(spacing)}${formattedAmount} at ${rateInPercent}`);
    }
  });
}

function displayDetailedBreakdown(income) {
  const cpp = calcBracketsTotal(calcBracketBreakdown(CPP_BRACKETS)(income));
  const ei = calcBracketsTotal(calcBracketBreakdown(EI_BRACKETS)(income));
  const federalTaxBreakdown = calcBracketBreakdown(FEDERAL_TAX_BRACKETS)(income);
  const federalTax = calcBracketsTotal(federalTaxBreakdown);
  const onTaxBreakdown = calcBracketBreakdown(ON_TAX_BRACKETS)(income);
  const onTax = calcBracketsTotal(onTaxBreakdown);
  const totalTax = federalTax + onTax;
  const surtax = calcBracketsTotal(calcBracketBreakdown(ON_SURTAX_BRACKETS)(onTax));
  const totalOwing = cpp + ei + totalTax + surtax;
  

  console.log('CPP:', formatDollars(cpp));
  console.log('EI:', formatDollars(ei));

  console.log(''); // break

  console.log('Federal Tax:', formatDollars(federalTax));
  displayBracketBreakdown(federalTaxBreakdown);

  console.log(''); // break

  console.log('Provincial Tax:', formatDollars(onTax));
  displayBracketBreakdown(onTaxBreakdown);

  if (surtax) {
    console.log('Surtax:', formatDollars(surtax));
  }

  console.log(''); // break

  console.log('Total:', formatDollars(totalOwing));
  console.log('Average rate:', formatPercent(totalOwing / income));
}

displayDetailedBreakdown(INCOME);