American odds, implied probability and the vig — the three ideas every line on a sportsbook is built from.
American odds in one paragraph
A minus number is what you must stake to win $100: at −110 you risk $110 to win $100. A plus number is what $100 of stake wins: at +150 you risk $100 to win $150. That is the whole encoding — everything else about a betting line is probability wearing that costume.
Implied probability
Every price converts to a break-even probability: implied % = 100 / (decimal odds). At −110 you need 52.4% just to tread water; at +150 you need 40%. If your true win probability is above the implied number, the bet has positive expected value; below it, the book keeps your money over time — no matter how often any single bet lands.
The vig — why both sides add past 100%
Price both sides of a spread at −110 and the implied probabilities sum to 104.8%. That extra 4.8% is the vig — the bookmaker's margin. De-vigging (rescaling both sides to sum to 100%) recovers the market's actual opinion, which is the number our model compares itself against on Best Bets.
Lines move — and differ by book
The same game is priced differently across books, in both line and price. A half point on a spread or three cents on a moneyline is real money over a season, which is why line shopping — always taking the best available price — is the one betting edge that requires no model at all.
Put it to work
- Odds Board Every book side by side, best price highlighted.
- Best Bets Where the model disagrees with the de-vigged market.