# Math.round()

The `Math.round()` function returns the value of a number rounded to the nearest integer.

## Syntax

`Math.round(x)`

`x`
A number.

### Return value

The value of the given number rounded to the nearest integer.

## Description

If the fractional portion of the argument is greater than 0.5, the argument is rounded to the integer with the next higher absolute value. If it is less than 0.5, the argument is rounded to the integer with the lower absolute value.  If the fractional portion is exactly 0.5, the argument is rounded to the next integer in the direction of +∞.  Note that this differs from many languages' `round()` functions, which often round this case to the next integer away from zero, instead giving a different result in the case of negative numbers with a fractional part of exactly 0.5.

Because `round()` is a static method of `Math`, you always use it as `Math.round()`, rather than as a method of a `Math` object you created (`Math` has no constructor).

## Examples

```Math.round( 20.49); //  20
Math.round( 20.5 ); //  21
Math.round( 42   ); //  42
Math.round(-20.5 ); // -20
Math.round(-20.51); // -21```

## Demonstrative Implementation

Below is a snippet of code that is functionally equivelent to math.round except that the snippet of code below is slower than Math.round. The purpose of the snippet of code below is to demonstrate how Math.round works.

```function vanilla_round(x) {
var y = +x + 0.5; // so that less than 1/2 rounds down; greater rounds up
return y - (y % 1);
}```

The modulus operator above gets the decimal part of x. Further, the above code snippet could be extended to round to a certain precision on a number:

```function round_to_precision(x, precision) {
var y = +x + (precision === undefined ? 0.5 : precision/2);
return y - (y % (precision === undefined ? 1 : +precision));
}```

Examples:

```round_to_precision(11, 2); // outputs 12
round_to_precision(11, 3); // outputs 12
round_to_precision(11, 4); // outputs 12
round_to_precision(11, 5); // outputs 10
round_to_precision(11, 6); // outputs 12
round_to_precision(11, 7); // outputs 14
round_to_precision(11, 8); // outputs 8
round_to_precision(3.7, 0.5); // outputs 3.5
round_to_precision(3.75, 0.5); // outputs 4
round_to_precision(3.8, 0.5); // outputs 4
```

## Specifications

Specification Status Comment
ECMAScript 1st Edition (ECMA-262) Standard Initial definition. Implemented in JavaScript 1.0.
ECMAScript 5.1 (ECMA-262)
The definition of 'Math.round' in that specification.
Standard
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'Math.round' in that specification.
Standard
ECMAScript Latest Draft (ECMA-262)
The definition of 'Math.round' in that specification.
Draft

## Browser compatibility

Update compatibility data on GitHub
Desktop Mobile Server Chrome Edge Firefox Internet Explorer Opera Safari Android webview Chrome for Android Firefox for Android Opera for Android Chrome Full support Yes Edge Full support 12 Firefox Full support 1 IE Full support Yes Opera Full support Yes Safari Full support Yes WebView Android Full support Yes Chrome Android Full support Yes Firefox Android Full support 4 Opera Android Full support Yes Safari iOS Full support Yes Samsung Internet Android Full support Yes nodejs Full support Yes

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