How the EV formula works
Expected value is what a bet earns on average if you could make it a thousand times: (decimal odds × win probability) − 1. Positive means the price pays more than the risk deserves. Negative means the book keeps the difference.
How to find your true win probability
The hard part isn't the formula, it's the win probability. That's the entire game. Big Mike's engine estimates it by de-vigging the market across books to find the consensus fair price, then flagging the books whose posted number beats it — the same math behind The Edge board on this site.
What counts as a good edge
Real edges in liquid markets are small: 1-2% is routine, 3-5% is strong, and double digits should make you re-check the win probability rather than raise the stake. Small positive numbers, taken relentlessly, are the whole business.
