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Discount Calculator

Sale-price calculator handling stacked discounts and tax.

shopping
30 downloads

By Lucas

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name: Discount Calculator description: "Sale-price calculator handling stacked discounts and tax." category: shopping connections: [] version: 1

What it does

Enter an original price plus up to two sequential discounts and an optional tax rate, and it shows the final price, total pre-tax savings, and a per-step breakdown of how each discount reduced the price. Discounts apply one after the other (20% then 10% is 28% off, not 30%), with live recalculation as you type and quick-pick discount buttons.

Setup

  • Open app.html directly in a browser (double-click the file, or serve the folder) — no build step, no internet needed.
  • Type the original price, first and second discount percentages, and optionally a tax percentage; results update instantly.
  • No persistence: values reset to defaults ($100, 20%, 10%, 0% tax) on reload.

Source

app.html — the complete app (single self-contained file: HTML, CSS, and JavaScript, no external dependencies):

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Discount Calculator</title>
<style>
  :root{
    --bg:#0f1b2d;
    --card:#16263e;
    --ink:#f2f5fa;
    --muted:#93a3b8;
    --accent:#35d0a5;
    --accent-ink:#06281e;
    --line:#27405f;
    --input:#0d1728;
  }
  *{box-sizing:border-box;margin:0;padding:0}
  body{
    font-family:-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,Helvetica,Arial,sans-serif;
    background:radial-gradient(1200px 600px at 50% -10%, #1b3050 0%, var(--bg) 55%);
    color:var(--ink);line-height:1.45;min-height:100vh;
    padding:24px 14px 60px;
  }
  .wrap{max-width:520px;margin:0 auto}
  header{text-align:center;margin-bottom:20px}
  header h1{font-size:1.9rem;letter-spacing:-0.02em}
  header p{color:var(--muted);font-size:.95rem;margin-top:4px}
  .card{
    background:var(--card);border:1px solid var(--line);border-radius:16px;
    padding:18px;margin-bottom:14px;
  }
  .card h2{font-size:1rem;margin-bottom:12px;color:var(--muted);text-transform:uppercase;letter-spacing:.08em;font-size:.75rem}
  .field{margin-bottom:14px}
  .field:last-child{margin-bottom:0}
  label{display:block;font-size:.85rem;color:var(--muted);margin-bottom:6px}
  .input-wrap{position:relative}
  .input-wrap .unit{
    position:absolute;right:14px;top:50%;transform:translateY(-50%);
    color:var(--muted);font-size:1rem;pointer-events:none;
  }
  input{
    width:100%;padding:12px 40px 12px 14px;font-size:1.15rem;border:1px solid var(--line);
    border-radius:10px;background:var(--input);color:var(--ink);
  }
  input:focus{outline:2px solid var(--accent);outline-offset:0;border-color:var(--accent)}
  .quick{display:flex;gap:8px;flex-wrap:wrap;margin-top:8px}
  .quick button{
    background:var(--input);border:1px solid var(--line);color:var(--muted);
    border-radius:20px;padding:6px 14px;font-size:.85rem;cursor:pointer;
  }
  .quick button:hover{color:var(--ink);border-color:var(--accent)}
  .hero{
    text-align:center;padding:22px 16px;
    background:linear-gradient(135deg,#12362b,#0f2c3a);
    border:1px solid #1f5c46;
  }
  .hero .label{font-size:.75rem;text-transform:uppercase;letter-spacing:.1em;color:var(--accent)}
  .hero .final{font-size:3rem;font-weight:800;letter-spacing:-0.03em;margin:6px 0}
  .hero .savings{font-size:1.05rem;color:var(--accent);font-weight:600}
  .breakdown{display:grid;gap:9px;font-size:.98rem}
  .line{display:flex;justify-content:space-between;gap:10px}
  .line .k{color:var(--muted)}
  .line .v{font-variant-numeric:tabular-nums;font-weight:600}
  .line.total{border-top:1px solid var(--line);padding-top:9px;font-size:1.1rem}
  .line.total .v{color:var(--accent)}
  .note{font-size:.82rem;color:var(--muted);text-align:center;margin-top:10px}
  .neg{color:#ff9d9d}
</style>
</head>
<body>
<div class="wrap">
  <header>
    <h1>Discount Calculator</h1>
    <p>Stacked discounts and tax, calculated the honest way.</p>
  </header>

  <div class="card">
    <h2>Inputs</h2>
    <div class="field">
      <label for="price">Original price</label>
      <div class="input-wrap">
        <input id="price" type="number" min="0" step="0.01" value="100" inputmode="decimal" oninput="recalc()">
        <span class="unit">$</span>
      </div>
    </div>
    <div class="field">
      <label for="disc1">First discount</label>
      <div class="input-wrap">
        <input id="disc1" type="number" min="0" max="100" step="0.1" value="20" inputmode="decimal" oninput="recalc()">
        <span class="unit">%</span>
      </div>
      <div class="quick">
        <button type="button" onclick="setDiscount('disc1', 0)">0%</button>
        <button type="button" onclick="setDiscount('disc1', 10)">10%</button>
        <button type="button" onclick="setDiscount('disc1', 20)">20%</button>
        <button type="button" onclick="setDiscount('disc1', 30)">30%</button>
        <button type="button" onclick="setDiscount('disc1', 50)">50%</button>
      </div>
    </div>
    <div class="field">
      <label for="disc2">Second discount (applied after the first)</label>
      <div class="input-wrap">
        <input id="disc2" type="number" min="0" max="100" step="0.1" value="10" inputmode="decimal" oninput="recalc()">
        <span class="unit">%</span>
      </div>
      <div class="quick">
        <button type="button" onclick="setDiscount('disc2', 0)">0%</button>
        <button type="button" onclick="setDiscount('disc2', 5)">5%</button>
        <button type="button" onclick="setDiscount('disc2', 10)">10%</button>
        <button type="button" onclick="setDiscount('disc2', 15)">15%</button>
      </div>
    </div>
    <div class="field">
      <label for="tax">Sales tax (optional)</label>
      <div class="input-wrap">
        <input id="tax" type="number" min="0" max="100" step="0.1" value="0" inputmode="decimal" oninput="recalc()">
        <span class="unit">%</span>
      </div>
    </div>
  </div>

  <div class="card hero">
    <div class="label">You pay</div>
    <div class="final" id="finalPrice">$0.00</div>
    <div class="savings" id="savingsLine">You save $0.00</div>
  </div>

  <div class="card">
    <h2>Breakdown</h2>
    <div class="breakdown">
      <div class="line"><span class="k">Original price</span><span class="v" id="lineOriginal">$0.00</span></div>
      <div class="line"><span class="k" id="lineD1Label">After 1st discount</span><span class="v neg" id="lineD1">$0.00</span></div>
      <div class="line"><span class="k" id="lineD2Label">After 2nd discount</span><span class="v neg" id="lineD2">$0.00</span></div>
      <div class="line"><span class="k">Discount savings (pre-tax)</span><span class="v" id="lineSaved">$0.00</span></div>
      <div class="line"><span class="k" id="lineTaxLabel">Tax</span><span class="v" id="lineTax">$0.00</span></div>
      <div class="line total"><span class="k">Final price (with tax)</span><span class="v" id="lineFinal">$0.00</span></div>
    </div>
    <p class="note">Discounts apply sequentially: 20% then 10% is 28% off, not 30%.</p>
  </div>
</div>

<script>
"use strict";

function num(id) {
  var v = parseFloat(document.getElementById(id).value);
  return isNaN(v) ? 0 : Math.max(0, v);
}

function clampPct(v) {
  return Math.min(100, Math.max(0, v));
}

function money(n) {
  return "$" + n.toFixed(2);
}

function setDiscount(id, value) {
  document.getElementById(id).value = value;
  recalc();
}

function recalc() {
  var original = num("price");
  var d1 = clampPct(num("disc1"));
  var d2 = clampPct(num("disc2"));
  var taxPct = clampPct(num("tax"));

  // Sequential: apply one after the other (NOT additive)
  var afterFirst = original * (1 - d1 / 100);
  var afterSecond = afterFirst * (1 - d2 / 100);
  var savedPreTax = original - afterSecond;
  var taxAmount = afterSecond * (taxPct / 100);
  var final = afterSecond + taxAmount;

  document.getElementById("finalPrice").textContent = money(final);
  document.getElementById("savingsLine").textContent =
    "You save " + money(savedPreTax) + " before tax";

  document.getElementById("lineOriginal").textContent = money(original);
  document.getElementById("lineD1Label").textContent =
    "After " + d1 + "% discount (" + money(original - afterFirst) + " off)";
  document.getElementById("lineD1").textContent = money(afterFirst);
  document.getElementById("lineD2Label").textContent =
    "After extra " + d2 + "% (" + money(afterFirst - afterSecond) + " off)";
  document.getElementById("lineD2").textContent = money(afterSecond);
  document.getElementById("lineSaved").textContent = money(savedPreTax);
  document.getElementById("lineTaxLabel").textContent = "Tax (" + taxPct + "%)";
  document.getElementById("lineTax").textContent = money(taxAmount);
  document.getElementById("lineFinal").textContent = money(final);
}

recalc();
</script>
</body>
</html>


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