Odds-on and odds-against: what they mean in numbers
Odds-on means a winning bet pays less than double the stake: decimal odds below 2.00, fractional odds below 1/1, implied probability above 50%. Odds-against is the reverse: above 2.00, above 1/1, below 50%. Evens is 2.00, 1/1 and 50%.
Definition
Odds-on and odds-against describe which side of the doubling line a price sits on. A price is compared with evens, where a winning bet returns exactly twice the stake. In decimal form that is 2.00, in fractional form 1/1, and the implied probability is 50%.
Odds-on prices are below 2.00, so the implied probability is above 50%. Odds-against prices are above 2.00, so it is below 50%. The conversion method is set out step by step in the guide on converting odds to implied probability.
| Fractional | Decimal | Implied probability | Label |
|---|---|---|---|
| 1/4 | 1.25 | 80.00% | odds-on |
| 1/2 | 1.50 | 66.67% | odds-on |
| 1/1 | 2.00 | 50.00% | evens |
| 6/4 | 2.50 | 40.00% | odds-against |
| 2/1 | 3.00 | 33.33% | odds-against |
| 4/1 | 5.00 | 20.00% | odds-against |
Illustrative example
A stake of KES 1,000 at odds-on 1/2 (decimal 1.50) returns 1,000 × 1.50 = KES 1,500 if it wins, which is KES 500 of profit. A stake of KES 1,000 at odds-against 2/1 (decimal 3.00) returns KES 3,000, which is KES 2,000 of profit. A losing bet in either case returns nothing, and the difference between return and profit is explained in the guide on stake, return and profit.
Read the percentage with care
These percentages are implied probabilities, and they include the bookmaker's margin. They are not true chances. The size of that margin is worked out in the guide on calculating the bookmaker's margin.
The break-even view helps. At 1.50 a selection must win 66.67% of the time just to return the stakes, so odds-on prices need frequent wins to avoid a loss, and one defeat erases several wins. Odds-against prices lose more often than they win, and the same arithmetic applies.
Safer-play note
Neither label makes a bet safer. Decide a stake you can afford to lose before looking at the price, and keep it inside your budget and limits. Section 71(1) of the Gambling Control Act, 2025 says a player in an online gambling activity shall not bet less than twenty shillings in a competition; see the note on the minimum online stake.
Questions and answers
Does odds-on mean the selection is likely to win?
Not by itself. Odds-on means the implied probability of the price is above 50%, but that figure includes the bookmaker's margin, so the true chance the price was built on is somewhat lower.
Is 1/2 the same as 1.50?
Yes. Fractional 1/2 is 1 divided by 2 = 0.50 of profit per shilling, and adding the stake back gives 1.50. The implied probability is 1 divided by 1.50 = 66.67%.
Why do odds-on prices still lose money on average?
Because a price at 1.50 only breaks even if the selection wins 66.67% of the time. Margin means the true win rate behind the price is lower than that, so the average result of the stake is a loss.