How I Built a Chrome Extension for Smarter Betting: The Value Bet Calculator

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 Vanilla JavaScript Manifest V3 (for Chrome compatibility) HTML / CSS (no frameworks) 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: ⚽ Football Livescore

Apr 21, 2025 - 12:50

How I Built a Chrome Extension for Smarter Betting: The Value Bet Calculator

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:

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
}