JavaScript Math round(): How It Works With Examples

JavaScript gives you the Math.round() function to deal with decimal numbers. You use it when you want to round a number to the nearest whole value. This helps when you show prices, handle points, or set limits. Developers use Math.round to fix float values in a clean and simple way.

Understand JavaScript Math.round()

Math.round() gives you the closest integer to a number. It follows normal rounding rules. Numbers above .5 go up. Numbers below .5 go down.

Here is the syntax:

Math.round(number)

The function takes one number. It returns a new number. The result does not change the original value.

JavaScript checks the decimal part. It looks at the first digit after the dot. If the digit is 5 or more, it moves the number up. If the digit is less than 5, it drops the decimal part.

Here is quick examples:

Math.round(7.3)

This gives you 7. The decimal is below .5. The function removes it and keeps the base number.

Math.round(7.7)

This gives you 8. The decimal is above .5. The function adds one to the base number.

Here are use cases:

• Show prices as whole numbers in a shop.
• Count points in a game.
• Handle distance in a GPS app.
• Reduce float errors in math output.
• Set score thresholds for a pass or fail.

So, how JavaScript Math.round() handles decimal values?

1- Numbers above and below .5:

JavaScript rounds down if the decimal part is less than 0.5. It rounds up if the decimal part is more than 0.5.

2- Exact .5 cases:

If the decimal part is exactly 0.5, the number moves up. Math.round(4.5) gives you 5. Math.round(-2.5) gives you -2. This stays true for both positive and negative values.

3- Rounding vs truncating:

Math.round(4.7) gives 5. Math.trunc(4.7) gives 4. The first moves to the nearest whole value. The second removes the decimal without rounding.

Examples of Math.round() in JavaScript

Round positive numbers:

Math.round(6.2) // 6  
Math.round(6.8) // 7

These round to the nearest whole values.

Round negative numbers:

Math.round(-3.2) // -3  
Math.round(-3.8) // -4

This works the same way as positive numbers.

Round Zero and Edge Values:

Math.round(0.4)  // 0  
Math.round(0.5)  // 1  
Math.round(-0.5) // 0  
Math.round(-0.6) // -1

Zero follows the same rules. The decimal part still controls the result.

Browser Support for Math.round()

You can use Math.round() in all modern browsers without issues. The method belongs to the core JavaScript standard. Every major engine includes it. You get full support across desktop and mobile platforms.

Here is a list of supported browsers:

• Google Chrome supports it from version 4 and later.
• Mozilla Firefox supports it from version 2 and later.
• Microsoft Edge includes support starting from version 12.
• Apple Safari supports it from version 3.1 and later.
• Opera includes it from version 10 and later.
• Internet Explorer supports it from version 6, though modern use is rare.
• Mobile versions of Chrome, Safari on iOS, Firefox for Android, and other mobile browsers also support it.

Any browser that runs JavaScript supports Math.round(). You do not face problems with compatibility.

Wrapping Up

In this article, you learned how JavaScript Math.round() works. You also learned how it handles decimal values, special cases, and different kinds of numbers.

Here is a quick recap:

• Math.round() gives the nearest whole number from a decimal value.
• It moves the number up if the decimal is .5 or more.
• It moves the number down if the decimal is less than .5.
• The function takes one number and returns a new rounded value.
• It does not change the original number.
• Math.round(7.3) gives 7. Math.round(7.7) gives 8.
• Use it to show whole prices, score points, or remove float errors.
• JavaScript rounds .5 up for both positive and negative values.
• Math.round(4.7) gives 5. Math.trunc(4.7) gives 4.
• Math.round(6.2) gives 6. Math.round(6.8) gives 7.
• Math.round(-3.2) gives -3. Math.round(-3.8) gives -4.
• Math.round(0.4) gives 0. Math.round(0.5) gives 1. Math.round(-0.5) gives 0. Math.round(-0.6) gives -1.

FAQs

Math.round(2.456 * 100) / 100  // gives 2.46