# How to fix decimals arithmetic in JavaScript

Find out how to fix decimals arithmetic in JavaScript

If you try to do the sum of two decimal numbers in JavaScript you might have a surprise.

`0.1 + 0.1` is, as you expect, `0.2`

But sometimes you have some unexpected result.

Like for `0.1 + 0.2`.

The result is not `0.3` as you'd expect, but it's `0.30000000000000004`.

Or `1.4 - 1`, the result is `0.3999999999999999` I'm sure your question is: WHY?

First, this is not unique to JavaScript. It's the same for every programming language.

The reason is due to the fact computers store data as binary, `0` or `1`.

Any value is represented in the binary numeric system, as a power of two.

1 is 1 * 2^0

10 is 1 * 2^1 + 0 * 2^0

Not every decimal number can be represented perfectly in this binary format, because some numbers are repeating numbers in binary. Try to convert 0.1 from decimal to binary.

Long story short, we'd need infinite precision to represent 0.1, and while computers can approximate that well, when we do calculations we lose some data since we need to "cut" somewhere, and this leads to those unexpected results you see above.

You can use libraries like decimal.js, bignumber.js or big.js.

You can also use a "trick" like this.

You decide to cut decimals after 2 positions, for example, and multiply the number by 100 to remove the decimal part.

Then you divide by 100 after you've done the sum:

``````0.1 + 0.2 //0.30000000000000004

(0.1.toFixed(2) * 100 + 0.2.toFixed(2) * 100) / 100 //0.3
``````

Use `10000` instead of `100` to keep 4 decimal positions.

More abstracted:

``````const sum = (a, b, positions) => {
const factor = Math.pow(10, positions)
return (a.toFixed(positions) * factor + b.toFixed(positions) * factor) / factor
}

sum(0.1, 0.2, 4) //0.3
``````

THE VALLEY OF CODE

THE WEB DEVELOPER's MANUAL

You might be interested in those things I do:

• Learn to code in THE VALLEY OF CODE, your your web development manual
• Find a ton of Web Development projects to learn modern tech stacks in practice in THE VALLEY OF CODE PRO
• I wrote 16 books for beginner software developers, DOWNLOAD THEM NOW
• Every year I organize a hands-on cohort course coding BOOTCAMP to teach you how to build a complex, modern Web Application in practice (next edition February-March-April-May 2024)
• Learn how to start a solopreneur business on the Internet with SOLO LAB (next edition in 2024)
• Find me on X