Five small tools. Everything is computed in your browser, and nothing you type is sent anywhere. To score a whole file of bets against real closing lines, use the closing line value tool.
Enter the American odds for both sides of a two-way market. The implied probabilities add up to more than 100 percent because of the book's margin; the no-vig figures remove it.
Enter two or three prices for every outcome of one market. Hold is how far the implied probabilities exceed 100 percent, shared out as the book's margin.
Enter the price you took and both sides of the closing line. The result is your expected return at the no-vig close: positive means your price was better than the close.
Enter two prices for the same outcome, from two books or two venues. The gap is the difference in implied probability, in percentage points.
A two-way bet pays at its price when your side wins, and loses the stake when it does not. On a spread or total set at a whole number, landing exactly on the number is a push: the stake is returned and no price is paid.
A prediction-market contract pays a fixed amount if the event happens and nothing if it does not. Its price, as a share of that payout, reads as the market's implied probability. You can usually sell a contract before the event settles, at whatever the market pays at that moment.
General descriptions only. Each book and exchange publishes its own settlement rules, and those rules govern.