Odds against
Odds against is any price longer than evens, where your potential profit is bigger than your stake because the bookmaker rates the outcome as less likely than not. In fractional form the first number is larger than the second, as in 5/2 or 7/1. In decimal form the price sits above 2.00. You will see it on most selections in a horse race and on outsiders in GAA and football markets, and reading it correctly starts with turning the fraction into a percentage.
How do you work out odds against?
A fractional price of a/b against means the bookmaker pays a units of profit for every b units you stake, and your stake comes back on top. The implied probability is b ÷ (a + b), which is the same as 1 divided by the decimal price.
Take 3/1 on a horse at Leopardstown. The sum is 1 ÷ (3 + 1), so the price implies a 25 per cent chance, and a €10 bet returns €40 if it wins: €30 profit plus your tenner back.
Converting to decimal is just as quick, because the decimal price equals (a + b) ÷ b, so 3/1 becomes 4.00 and 5/2 becomes 3.50.
The phrase itself comes from the old way of saying a price aloud. Bookmakers in Ireland and Britain still read 4/1 as “four to one against”, meaning four ways to lose for every one way to win at the quoted price, although the word against is usually dropped on a betting slip. Evens, 1/1 or 2.00, is the dividing line: the price implies exactly 50 per cent, and anything longer is odds against while anything shorter is odds-on.
Odds against versus odds-on
The term most often confused with odds against is its mirror image, odds-on. An odds-on price such as 1/2 pays less profit than you staked, because the outcome is rated more likely than not; 1/2 works out at 2 ÷ 3, or about 66.7 per cent.
The two are reciprocals of each other, which is why a price can be described either way. Saying a team is 2/1 against to win is the same as saying the market thinks it is 1/2 on to lose, at least before any margin is taken into account.
Margin matters here.
The implied probabilities across a whole market add up to more than 100 per cent, and the excess is the bookmaker’s overround. So the 25 per cent you read from a 3/1 price is the bookmaker’s figure with its margin built in, and it is a little higher than the fair chance the market would show without that margin. How large the overround is varies between operators and between markets, so we read it off the prices on the day rather than assuming a standard figure.
Common prices against, converted
The rows below take five familiar prices longer than evens and convert each into decimal form, implied probability and the return on a €10 stake. Every figure comes straight from the formulas above, with the stake included in the return.
| Fractional price | Decimal price | Implied probability | €10 bet returns |
|---|---|---|---|
| 6/5 | 2.20 | 45.5% | €22.00 |
| 2/1 | 3.00 | 33.3% | €30.00 |
| 5/2 | 3.50 | 28.6% | €35.00 |
| 5/1 | 6.00 | 16.7% | €60.00 |
| 10/1 | 11.00 | 9.1% | €110.00 |
Where you meet odds against
Most of a racecard is odds against, because a field of ten or more runners can only hold one or two horses at odds-on. Each-way bets lean on these prices, since the place part pays a fraction of the win odds, commonly a quarter or a fifth depending on the race and the bookmaker’s terms.
In football and GAA you meet it on the draw, on the underdog and on most bet builder and accumulator selections. An acca multiplies decimal prices together, so four selections at 3.00 combine to 81.00, which implies a chance of roughly 1.2 per cent.
Free bets are where the sum shifts again. With a free bet the stake is not returned, so a €10 free bet at 4/1 pays €40 in winnings and nothing more, which is why longer prices tend to suit free bet stakes.
What I check first on any price against is the implied percentage, because a long number looks generous until you see how small a chance it actually describes.
