What is Odds-Against?

How Odds-Against Works

Odds-against simply means the numerator (the first number in a fractional price) is larger than the denominator. At 2/1, you win £2 for every £1 you risk; at 5/2, you win £2.50 for every £1. In decimal format, any price above 2.0 is odds-against. The implied probability of an odds-against selection is always below 50%, which is why bookmakers will often price most outcomes in a typical two-runner market at odds-against rather than odds-on — their overround ensures both sides sit at a combined implied probability above 100%.

It is worth understanding this in terms of implied probability. To convert fractional odds to an implied probability, divide the denominator by the sum of both numbers and multiply by 100. So 3/1 gives (1 ÷ 4) × 100 = 25%. At 6/4, it is (4 ÷ 10) × 100 = 40%. Any result below 50% confirms the selection is odds-against. The further the implied probability falls below 50%, the longer the odds and the greater the theoretical reward relative to the stake.

Worked Example

Suppose a tipster advises a football team to win at 7/2 (decimal 4.50). This is odds-against because 7 is greater than 2, and the implied probability is (2 ÷ 9) × 100 = 22.2%. A £10 stake returns £35 profit plus your £10 stake back, giving total returns of £45. If you had taken the same team at 5/2 instead, a £10 stake would return only £25 profit — the advised price of 7/2 therefore represents better value for the same successful outcome.

This straightforward arithmetic is why recording the odds at which a tipster advises bets — known as advised odds — matters so much. A tipster who consistently obtains odds-against prices that exceed the true probability of an event winning is, over time, demonstrating positive expected value. If their advised prices are routinely clipped by the time you come to place the bet, the financial benefit of those longer odds-against prices is eroded.

Why It Matters When Judging a Tipster

When reviewing a tipster's record on TipsterCheck, odds-against selections are the building blocks of long-term profitability. A tipster with a strike rate of 30% can still generate a healthy yield if their winners are consistently taken at fair or better odds-against prices. Conversely, a tipster winning 50% of bets can still show a loss if they are regularly taking odds-on or marginal odds-against prices that do not reflect the true probability of success. Looking at the distribution of advised prices is therefore essential context for any published results.

Odds-against also interacts directly with closing line value (CLV) — a key measure of tipster skill. If a tipster advises a selection at 4/1 and the market shortens to 5/2 by the time the event starts, the original price was clearly better value relative to the market's final assessment. Tracking whether a tipster's advised odds-against prices hold up or drift further signals whether their edge is genuine. Be cautious of any service that does not record or publish the odds at which bets were advised, as without that data it is impossible to verify whether returns are replicable.

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