Percentage Calculator - Percent Change, Margin & Markup Online

// Percentage calculations in JavaScript

// What is X% of Y?
function whatIsPercentOf(percent, base) {
  return base * (percent / 100);
}
console.log(whatIsPercentOf(15, 200));    // 30

// X is what % of Y?
function whatPercentIsXOfY(value, total) {
  if (total === 0) throw new Error('Total cannot be zero');
  return (value / total) * 100;
}
console.log(whatPercentIsXOfY(30, 200));   // 15

// X is Y% of what?
function xIsPercentOfWhat(value, percent) {
  if (percent === 0) throw new Error('Percentage cannot be zero');
  return value / (percent / 100);
}
console.log(xIsPercentOfWhat(30, 15));     // 200

// Percentage change
function percentageChange(oldValue, newValue) {
  if (oldValue === 0) throw new Error('Old value cannot be zero');
  return ((newValue - oldValue) / Math.abs(oldValue)) * 100;
}
console.log(percentageChange(50, 75));     // 50
console.log(percentageChange(75, 50));     // -33.333...

// Percentage increase / decrease
function percentageIncrease(original, percent) {
  return original * (1 + percent / 100);
}
function percentageDecrease(original, percent) {
  return original * (1 - percent / 100);
}
console.log(percentageIncrease(200, 15));  // 230
console.log(percentageDecrease(200, 15));  // 170

// Percentage difference
function percentageDifference(value1, value2) {
  const avg = (value1 + value2) / 2;
  if (avg === 0) return 0;
  return (Math.abs(value1 - value2) / avg) * 100;
}
console.log(percentageDifference(50, 75)); // 40

// Margin vs Markup
function marginAndMarkup(cost, revenue) {
  const profit = revenue - cost;
  const margin = revenue !== 0 ? (profit / revenue) * 100 : 0;
  const markup = cost !== 0 ? (profit / cost) * 100 : 0;
  return { profit, margin, markup };
}
console.log(marginAndMarkup(60, 100));
// { profit: 40, margin: 40, markup: 66.666... }