How to Format a Number with Decimals in JavaScript

To format a number with decimals in JavaScript, use the built-in toFixed method: (3.10391).toFixed(3) returns the string '3.104'. This guide covers toFixed, when it isn’t enough (truncation, locales, thousands separators), and the floating-point precision gotcha that catches people the first time.

Last verified: 2026-05-17 in Chromium, Firefox, Safari, and Node.js 22. Originally published 2023-03-19, rewritten and updated 2026-05-17.

TL;DR

(3.10391).toFixed(3);                     // "3.104"  (rounded)
parseFloat("3.10391").toFixed(3);          // "3.104"  (string in -> rounded string out)

// Need a number back?
Number((3.10391).toFixed(3));              // 3.104

// Need truncation, not rounding?
Math.floor(3.10391 * 1000) / 1000;         // 3.103

// Locale-aware + thousands separator?
new Intl.NumberFormat('en-US',
  { minimumFractionDigits: 3,
    maximumFractionDigits: 3 }
).format(1234567.891);                     // "1,234,567.891"

The toFixed method

toFixed(n) is a method on every JavaScript number. It returns a string representation rounded to n decimal places:

(3.10391).toFixed(3);     // "3.104"
(3.10391).toFixed(2);     // "3.10"
(3.10391).toFixed(0);     // "3"
(3.5).toFixed(0);         // "4"

If the value comes from a database or API as a string, wrap it in parseFloat first, since toFixed only exists on numbers:

const raw = "3.10391";       // e.g. from JSON
parseFloat(raw).toFixed(3);  // "3.104"

Round, floor, or ceil to N decimals

toFixed always rounds. If you specifically need truncation or ceiling, combine Math.floor / Math.ceil with a multiplier:

// Round (same as toFixed)
(Math.round(3.10391 * 1000) / 1000).toFixed(3);  // "3.104"

// Truncate
(Math.floor(3.10391 * 1000) / 1000).toFixed(3);  // "3.103"

// Ceiling
(Math.ceil(3.10391 * 1000) / 1000).toFixed(3);   // "3.104"

The * 1000 / 1000 shift is what controls the precision — three decimals here. For two decimals use * 100 / 100, for four use * 10000 / 10000.

The floating-point precision gotcha

JavaScript numbers are IEEE-754 floats, so 0.1 + 0.2 is internally 0.30000000000000004 — not 0.3. toFixed(2) rounds the display to '0.30', which is what you usually want for display. But strict equality (===) still fails:

0.1 + 0.2 === 0.3;                  // false
(0.1 + 0.2).toFixed(2);             // "0.30"
Number((0.1 + 0.2).toFixed(2)) === 0.30;  // true

For display, toFixed is fine. For money or any value where every cent matters, store integers (cents/satoshis) or use a decimal library like decimal.js — never trust the float for accounting.

Locale-aware formatting

toFixed always uses . as the decimal separator and never adds thousands separators. For user-facing display, Intl.NumberFormat handles both, in any locale:

const fmt = new Intl.NumberFormat('en-US', {
  minimumFractionDigits: 3,
  maximumFractionDigits: 3,
});
fmt.format(1234567.891);            // "1,234,567.891"

new Intl.NumberFormat('fr-FR',
  { minimumFractionDigits: 3,
    maximumFractionDigits: 3 }
).format(1234567.891);              // "1 234 567,891"

Built into every modern browser and Node.js — no dependency needed.

Frequently asked questions

Related guides

• How to Check if a JavaScript String Is a Valid URL
• How to Convert a String to Float in PHP

References

MDN Number.prototype.toFixed: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/toFixed. Intl.NumberFormat: developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/NumberFormat.