Number.prototype.toFixed()

toFixed(digits)

toFixed() formats a number to a specified number of decimal places, returning the result as a string. This is essential for financial calculations, currency display, and anywhere precise decimal control matters.

Syntax

num.toFixed(digits)

Parameters:

• digits — Number of decimal places (0 to 100). Values 0-20 are most widely supported.

Returns: A string representation of the number with exactly digits decimal places.

How It Works

toFixed() rounds the number to the specified precision rather than simply truncating it. The last digit is rounded according to standard rounding rules — if the next digit is 5 or greater, it rounds up.

(2.35).toFixed(1)   // "2.4" — rounds up
(2.34).toFixed(1)   // "2.3" — rounds down
(1.235).toFixed(2)  // "1.24" — rounds up
(1.234).toFixed(2)  // "1.23" — rounds down

Why It Returns a String

This is intentional. JavaScript’s number type follows IEEE 754 floating-point, which can’t precisely represent many decimal values. By returning a string, toFixed() preserves the formatted representation without introducing floating-point errors:

const price = 19.99;
const formatted = price.toFixed(2); // "19.99" (string)
// Use with currency symbols:
'$' + (9.99).toFixed(2)             // "$9.99"

Common Use Cases

Currency Formatting

const amounts = [19.99, 5.5, 100, 0.1];

amounts.forEach(amount => {
  console.log('$' + amount.toFixed(2));
});
// $19.99
// $5.50
// $100.00
// $0.10

Percentage Display

function formatPercent(value, total) {
  const percent = (value / total) * 100;
  return percent.toFixed(1) + '%';
}

formatPercent(7, 20)  // "35.0%"
formatPercent(1, 3)  // "33.3%"

Precision Control

const measurements = [1.23456, 9.8765, 0.001];

console.log(measurements.map(n => n.toFixed(2)));
// ["1.23", "9.88", "0.00"]

console.log((Math.PI).toFixed(4));  // "3.1416"

Limits and Compatibility

Digits	Support	Notes
0-20	✅ Universal	Works in all browsers and environments
21-100	⚠️ Varies	May throw RangeError in older environments

When digits is omitted, it defaults to 0:

(42).toFixed()     // "42"
(42.7).toFixed()   // "43" — rounds to whole number

Gotchas

Floating-Point Precision

Binary floating-point can’t exactly represent all decimals:

(0.3).toFixed(20)  // "0.29999999999999998890"

For critical financial work, consider using integer math or libraries like decimal.js.

Rounding Edge Cases

Some values exhibit floating-point rounding quirks:

(2.55).toFixed(1)  // "2.5" — should be "2.6" but precision limits prevent it

See Also

• number::toPrecision — Format to precision
• number::toString — Convert to string