You often hear a sporting event referred to as being “odds on”. The expression is even used in general conversation to explain that a particular event in life is regarded as a near certainty.
But what does the expression actually mean in practice?
Well, to understand what we mean by the phrase ‘odds on’, it’s first helpful to have an understanding of basic probability and how odds are expressed.
Let’s take the toss of two coins as an example. As long as the coins are true and aren’t damaged or biased in any way, the probability of predicting a toss correctly is a 50-50 chance – and when you toss the second coin, the same probability exists (regardless, of course, of what the first coin has done).
So, before either coin has been tossed, the chances of, let’s say, tails being tossed twice in a row are 1/2 x 1/2, which comes out as a one in four chance. Now, when expressed in bookmakers’ parlance as fractional odds, this is expressed as three to one against, i.e. there are three possible outcomes working “against” your tails-tails selection, which are tails-heads, heads-heads and heads-tails, so your selection is a 3-1 chance. Some bookmakers and punters prefer to use decimal odds, and the 3-1 shot would be simply expressed as four.
Now let’s consider the chances of tossing one heads and one tails in any coin combination. The chances of this outcome are 50-50 because it doesn’t matter what the first coin has done, the second one just needs to do the opposite. The chances are, therefore, one in two. Bookmakers would express this chance as being 1/1 or “evens”. Simply put, anything below evens (sometimes expressed as “even money”) would be deemed “odds on”, i.e, there is a greater chance of it happening than not.
So, to go back to our coins example, the probability of tails turning up on either of the coin tosses would be three from four (the possible combinations being heads-heads (lose), heads-tails (win), tails-heads (win), tails-tails (win). In probability terms, this would be expressed as a 3/4 or 75% chance of occurring – whilst a bookmaker would express this as being “odds on” at 1-3 (or 1.33 if expressed decimally).
In other words, for each £1 bet successfully at the odds-on chance of 1-3, you would make a profit of 33p because this is deemed significantly more likely to happen than not. So, “odds-on” simply means that – and is any price which is shorter than evens (1/1).