Round numeric results
Convert measured or calculated decimal values to whole-unit quantities.
JavaScript · Function
Math.round
Math.round() returns a number rounded to the nearest integer. Exact halves round toward positive infinity, so -3.5 becomes -3 and 3.5 becomes 4.
How it works
Math.round() converts its argument to a number and returns the closest integral Number. When two integers are equally close, it chooses the one toward positive infinity, so positive and negative halves behave differently.
Syntax
Math.round(x)Parameters
| Name | Type | Description |
|---|---|---|
x | number | The numeric value to round; it is converted to a Number before rounding. |
Returns
The value of x rounded to the nearest integer.
Key points
- Returns the input rounded to the nearest integer.
- Fractions above 0.5 round away from the current integer toward the next integer.
- Exact halves resolve toward positive infinity.
- Call it through Math.round(); it is not an instance method.
- The return value is a Number containing the rounded result.
Common mistakes
- Halfway values round toward positive infinity: 3.5 becomes 4, while -3.5 becomes -3.
- Do not replace Math.round(x) with Math.floor(x + 0.5), because results can differ, especially for negative zero.
- Values from -0.5 through values below zero can produce negative zero; use Object.is(result, -0) when the sign matters.
Example: Round values to integers
const values = [3.49, 3.5, -3.5, -0.1];
const rounded = values.map(Math.round);
console.log(rounded); // [3, 4, -3, -0]Maps Math.round over several values to show ordinary rounding, ties toward positive infinity, and preservation of negative zero.
When to use it
Nearest-integer decisions
Choose the nearest integer for display or threshold logic.
Signed numeric processing
Handle signed values while preserving JavaScript's negative-zero behavior when relevant.
Related
Math.ceil()Math.floor()Math.trunc()Object.is()