Put to the numbers, "value betting" begins with one idea. Value betting means backing a price that is higher than the true chance of the outcome deserves. The idea is simple to state and hard to use: every price carries the book's margin, so a bet has value only when the bettor's own estimate of the probability beats the price by more than that margin. Expected value is the arithmetic that says whether a given bet clears the bar or falls short.
How to calculate expected value betting in practice: turn the decimal odds into an implied probability by dividing one by the price, then compare it with the bettor's own estimate. Odds of 2.5 imply forty percent. If the estimate is forty five percent, the expected value is positive by roughly an eighth of the stake. The whole method rests on that estimate, which is where most value bettors go wrong.
Is value betting profitable? For a few careful and patient bettors, modestly and slowly, and for most, it never shows up at all. Is value betting legal? It is simply betting, legal wherever betting is, though books may limit or close accounts that win steadily. That limit is the real ceiling on value betting: an edge that the book notices tends to lose the stake size it needs to count.
Expected value betting starts from one line of arithmetic. Multiply the chance of winning by what a win returns, subtract the chance of losing times the stake, and the result is the average gain or loss per bet over many repeats. A bet at decimal odds of 2.2 on an outcome that lands half the time shows a small positive number; the same price on a forty percent chance shows a loss, however good the bet feels.
Dividing one by the decimal price gives the implied chance, so odds of 2.5 imply forty percent, and that figure is set against the bettor's own estimate.
Books may limit or close them, and that limit on stake size is the real ceiling on how much value betting can return.
Closing line value compares the price a bettor took with the final price before the start; beating it again and again is the clearest sign estimates are sound.
Only when the bettor's estimate of the chance beats the price by more than the margin the book builds into it.
Yes. A real but small edge can sit behind losing stretches for months, which is why short runs prove very little either way.