JavaScript Number Precision

Written by Swapnil RajaPublished 24 Aug 2026

Decimal arithmetic in JavaScript is not always exact, which is why 0.1 plus 0.2 is not 0.3.

This is not a JavaScript bug; it affects almost every language.

Numbers are stored in binary, and some decimals cannot be written exactly in binary.

Example

javascript

console.log(0.1 + 0.2);
console.log(0.1 + 0.2 === 0.3);

The output is 0.30000000000000004 then false.

The tiny error is real and it matters.

Why It Happens

Numbers are stored as binary fractions.

PreviousJavaScript parseInt and parseFloat NextJavaScript Math Object

Complete Example

html

<!DOCTYPE html>
<html>
<head>
  <title>JavaScript Number Precision</title>
</head>
<body>

  <h1>Number Precision</h1>

  <p id="out"></p>

  <script>
    const total = 0.1 + 0.2;

    document.getElementById("out").innerHTML =
      "0.1 + 0.2 = " + total +
      "<br>Equals 0.3: " + (total === 0.3) +
      "<br>Rounded: " + total.toFixed(2) +
      "<br>Close enough: " + (Math.abs(total - 0.3) < 0.0001) +
      "<br>In pence: " + ((10 + 20) / 100);
  </script>

</body>
</html>

JavaScript Number Precision

Example

Why It Happens

Syntax

Comparing Safely

Example

Rounding for Display

Example

Working in Whole Numbers

Example

Errors Accumulate

Example

Whole Numbers Are Exact

Example

Complete Example

Try It Yourself

Important Points

Conclusion