On a price screen, "What betting odds are good?" comes down to two numbers. Betting odds are a price and a forecast in one number. A short explanation covers most of it: the odds say how much a winning stake returns, and they hint at how likely the book thinks the outcome is. What does not show on the surface is the margin, which is why reading odds well means looking past the payout to the chance behind the price.
To interpret betting odds, turn the price into two numbers: the payout and the implied chance. At decimal odds of 3.00 a stake of ten returns thirty, so the betting odds payout is thirty with twenty of it profit. The implied chance is one in three. If the event happens more often than that over many tries, the price is generous; if less often, the price is short. Every other reading of a price rests on those two numbers.
A working definition of betting odds: the ratio between what a bet returns and what it risks, set by the book before the event. How odds work in betting follows from that. Short odds mean a likely outcome and a small return, long odds mean an unlikely one and a large return. What betting odds mean for a bettor is a trade: more potential payout always comes with less chance of collecting it, and the book's cut sits inside both sides of that trade.
Which betting odds are good depends on the gap between the price and the true chance, and the size of the number alone says little. Long odds on a pick that rarely wins are poor value, and short odds on a near certainty can be fair. A good price is one where the implied chance sits below the real one. Since no bettor knows the real chance exactly, most prices offered carry the margin and pay slightly less than fair.
A price on who wins outright, with the favourite at short odds and the underdog at a long price.
An odds table lines up formats side by side with implied chances, showing for instance that 1.50 means about sixty seven per cent and 11.00 about nine.
Only when the real chance of the outcome is higher than the chance the price implies; the size of the number alone says little.
Odds state how much a winning stake returns and hint at how likely the book rates the outcome, with its cut hidden inside.
Short odds point to a likely outcome and a small return, while long odds point to an unlikely one and a large return.