Betting odds explained simply: a price is a probability in disguise, with the bookmaker’s margin added on top. Once you can turn odds into the chance they imply, you can compare a price with your own view, or a model’s, and see whether it is generous or mean. This guide covers that conversion, the margin, the idea of value and the signals people use to judge whether they are getting good prices over time.
What Is Implied Probability?
Implied probability is the chance a price suggests: one divided by the decimal odds. Add up the implied probabilities of every outcome in a market and the total comes to more than one hundred per cent. The excess is the bookmaker’s margin, known in Britain as the overround.
Worked example: decimal odds of 2.50 imply 1 ÷ 2.50 = 40%. If a three-way market prices at 2.50, 3.40 and 3.00, the implied chances are about 40%, 29.4% and 33.3%, which add up to about 102.7%: the extra 2.7 points are the margin.
Is Vigorish the Same as Overround?
Yes. Vigorish, or juice, is the American term for the same thing: the amount by which a market’s implied probabilities exceed one hundred per cent. It is how a bookmaker earns regardless of the result, and it is the first thing to look at when comparing two prices for the same match.
What Do Odds-on and Odds-Against Mean?
Odds-on means a price shorter than even money: the implied chance is above one half and a winning bet returns less than the stake in winnings. Odds-against is the opposite, a price longer than evens. Neither says anything about value on its own; a short price can be generous and a long one mean.
What Is Expected Value?
Expected value is the average return a bet would give if it could be repeated many times: the chance of winning times what it pays, minus the chance of losing times the stake. A bet has positive expected value, or value, when your estimated chance is higher than the price implies after the margin. Everything depends on that estimate being right, which is why the betting calculator asks for your own probability.
What Is Closing Line Value?
Closing line value compares the price you took with the final price just before kick-off. Markets absorb information as the match approaches, so the closing price is usually the sharpest estimate available. Consistently getting better prices than the close is one of the few signs of skill that shows up before the results do; the TACTIX scoreboard reports the model against closing prices for the same reason.
What Is a Steam Move?
A steam move is a sudden shortening of a price across many bookmakers at once, driven by concentrated, well-informed money rather than casual bets. By the time most people notice it, the value that caused it has usually gone.
What Do Sharp and Square Mean?
A sharp is a bettor whose opinions move markets: disciplined about price and stakes, and accurate over time. A square is the casual counterpart, drawn to favourites, big names and recent form whatever the price. Bookmakers watch the first group closely and price partly for the second.
Where Betting Odds Explained Meets the Model
TACTIX publishes calibrated probabilities, so you can set a model’s chance beside a price and see the gap, while remembering that no estimate is exact. The accuracy page shows how well those probabilities have matched results, and the free-bets guide applies the same maths to promotions.
18+. Information and analysis only, not betting advice. If gambling stops being fun, free and confidential help is at BeGambleAware.org.
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