Simple Calculator Online – Free Basic Math Calculator

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Simple Calculator</title>

<style>
* {
    box-sizing: border-box;
}

.calculator {
    width: 100%;
    max-width: 300px;
    margin: 15px auto;
    padding: 15px;
    font-family: Arial, sans-serif;
    background: #ffffff;
    border: 1px solid #e2e8f0;
    border-radius: 12px;
    box-shadow: 0 3px 12px rgba(0,0,0,0.08);
}

.calculator h2 {
    text-align: center;
    font-size: 21px;
    color: #1e293b;
    margin: 0 0 14px;
}

#display {
    width: 100%;
    height: 50px;
    padding: 10px;
    margin-bottom: 12px;
    border: 1px solid #cbd5e1;
    border-radius: 7px;
    background: #f8fafc;
    font-size: 23px;
    text-align: right;
    color: #0f172a;
}

.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 7px;
}

.buttons button {
    height: 44px;
    border: none;
    border-radius: 7px;
    background: #e2e8f0;
    color: #1e293b;
    font-size: 18px;
    font-weight: 600;
    cursor: pointer;
}

.buttons button:hover {
    filter: brightness(0.95);
}

.buttons .operator {
    background: #dbeafe;
    color: #2563eb;
}

.buttons .clear {
    background: #fee2e2;
    color: #dc2626;
}

.buttons .equal {
    grid-column: span 2;
    background: #2563eb;
    color: white;
}

.more-calculators {
    display: block;
    margin-top: 12px;
    padding: 12px;
    border-radius: 7px;
    background: #2563eb;
    color: #ffffff;
    text-align: center;
    text-decoration: none;
    font-size: 14px;
    font-weight: 600;
}

.more-calculators:hover {
    background: #1d4ed8;
    color: white;
}

@media (max-width: 350px) {
    .calculator {
        padding: 10px;
    }

    .buttons button {
        height: 40px;
        font-size: 16px;
    }
}
</style>
</head>

<body>

<div class="calculator">

    <h2>Simple Calculator</h2>

    <input type="text" id="display"
           placeholder="0" readonly
           aria-label="Calculator display">

    <div class="buttons">

        <button class="clear" onclick="clearDisplay()">AC</button>
        <button onclick="deleteLast()">DEL</button>
        <button class="operator" onclick="appendValue('%')">%</button>
        <button class="operator" onclick="appendValue('/')">÷</button>

        <button onclick="appendValue('7')">7</button>
        <button onclick="appendValue('8')">8</button>
        <button onclick="appendValue('9')">9</button>
        <button class="operator" onclick="appendValue('*')">×</button>

        <button onclick="appendValue('4')">4</button>
        <button onclick="appendValue('5')">5</button>
        <button onclick="appendValue('6')">6</button>
        <button class="operator" onclick="appendValue('-')">−</button>

        <button onclick="appendValue('1')">1</button>
        <button onclick="appendValue('2')">2</button>
        <button onclick="appendValue('3')">3</button>
        <button class="operator" onclick="appendValue('+')">+</button>

        <button onclick="appendValue('0')">0</button>
        <button onclick="appendValue('.')">.</button>
        <button class="equal" onclick="calculate()">=</button>

    </div>

    <a href="https://calczila.com/" class="more-calculators">
        Check More Calculators →
    </a>

</div>

<script>
const display = document.getElementById("display");

function appendValue(value) {
    if (display.value === "Error") {
        display.value = "";
    }
    display.value += value;
}

function clearDisplay() {
    display.value = "";
}

function deleteLast() {
    display.value = display.value.slice(0, -1);
}

function calculate() {
    try {
        const expression = display.value;

        if (!expression || !/^[0-9+\-*/%.() ]+$/.test(expression)) {
            throw new Error("Invalid input");
        }

        const result = Function(
            '"use strict"; return (' + expression + ')'
        )();

        display.value = Number.isFinite(result)
            ? String(Number(result.toPrecision(12)))
            : "Error";

    } catch {
        display.value = "Error";
    }
}
</script>

</body>
</html>