# Using JavaScript Math.floor() method

Posted on Dec 28, 2020

Let's learn how JavaScript Math.floor() method works

The JavaScript `Math.floor()` method is a part of the Math object that you can use to round a decimal number down. For example, a number variable of `7.2` will be rounded down to `7` when you pass it into the method.

The syntax for this method looks as follows:

``````Math.floor(7.2); // returns 7
``````

You can pass the initial number as a variable:

``````let score = 7.2;

Math.floor(score); // returns 7
``````

Or store the returned number in a variable like this:

``````let score = 7.2;

let roundedScoreDown = Math.floor(score);

console.log(roundedScoreDown); // 7
``````

The method accepts only one parameter of `number` value. If you pass a `string`, an `object`, or an `array` to the method, it will return `NaN` which stands for `Not a Number`:

``````Math.floor("Hello there!");
Math.floor([1, 2, 3]);
Math.floor({ name: "Andy" });

// returns NaN
``````

When you pass a `boolean` value of `true` or `false` it will return `1` for `true` and `0` for `false`:

``````Math.floor(true);
// returns 1

Math.floor(false);
// returns 0
``````

Remember to use dot (`.`) when you pass in a decimal number because a comma (`,`) in JavaScript parameters is an indicator of separate variables. In the following example, JavaScript will simply floor the first number and ignore the second when you pass two numbers:

``````Math.floor(9, 2);

// returns 9
``````

Finally, the Math.floor() method will round a number down no matter if the decimal value is `.5` or higher:

``````Math.floor(8.5);

// returns 8
``````

## Using Math.floor() on negative numbers

The method will also round a negative number down. Negative numbers get smaller the farther they are from zero, so the number value of `-55.2` will be rounded to `-56` and not `-55`:

``````Math.floor(-55.2)

// returns -56
``````

## Other Math rounding method

Finally, if you want to round the number up when its decimal value is higher than `.5` then you need to use `Math.round()` method.

When you want to round the number up instead of down (from `7.2` to `8`) then you need to use [the `Math.ceil()` method]( {{ <ref “/18-javascript-math-ceil”> }} ).

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