The Idea

As a sports fan and data geek, I often wondered:

Is this bet actually worth it?

That’s how the Value Bet Calculator extension was born — a simple browser tool that helps you instantly calculate the expected value (EV) of a bet using the formula:

Value = (Estimated Probability × Bookmaker Odds) - 1

How It Works

You can use it in two modes:

  • Manual Mode – Just input your odds and estimated probability
  • Auto Mode – Select a match, and it pulls real-time data from the odds API

Here’s what the manual calculator looks like:

Calculate

And here’s the core logic:

function calculateValue(probability, odds) {
  const value = (probability / 100) * odds - 1;
  return Math.round(value * 1000) / 10; // round to 1 decimal
}

What It’s Built With

  1. Vanilla JavaScript
  2. Manifest V3 (for Chrome compatibility)
  3. HTML / CSS (no frameworks)
  4. Designed to work in Chrome, Firefox, Edge, and Opera

The extension is lightweight and doesn’t track or store personal data.

GitHub Pages Version (Try It Live!)

You can try the live version right here (no install needed):

Value Bet Calculator – Web Version

GitHub Repo

Feel free to fork or use the code in your own projects:
View on GitHub

Want to Learn More About Value Betting?

If you’re into football, basketball or hockey betting — check these:

Final Thoughts

This was a fun project that blends data, logic, and real-world use.

If you’re into building extensions or sports analytics tools, would love to hear your thoughts — or better yet, collaborate on the next version.

Thanks for reading!