What Chance Is That Price Really Giving My Horse?

Divide one by the decimal price. That is the whole conversion.

An evens shot gives one divided by two, or a half. A 4.0 shot is a quarter. A 13.0 shot, which is 12/1, is about one in thirteen. Working from fractions, add the two numbers together and divide the right one by that total: 12/1 becomes one in thirteen, the same answer.

So a price is a claim. When a bookmaker puts up 12/1, they are saying this horse wins about one time in thirteen. Yesterday we turned prices into money. Today we turn them into chances, because that is the number you need to judge whether a price is any good.

There is a catch, and it is the most useful thing on this page. Add up the implied chances of every runner in a race and the total comes to more than a whole. Nothing can happen more often than always, so the excess is not a statement about horses at all.

We checked every price against reality

Rather than argue about it, we counted. Across 218,437 British runners we took every price and asked two questions. What chance does this price imply, and how often did horses at that price actually win.

Read the middle two columns against each other. At the short end the market is close to honest. The last column is what a pound staked at that price returned.

The market is a good judge of horses. It is also an expensive place to have an opinion.

The longer the price, the worse the deal

Follow the last column of that table down. Odds-on shots lose 2.5% in the pound. By 20/1 to 32/1 it is 23.8%. At 100/1 and longer it is 62.7%.

This is the most useful pattern in the table, and it runs against instinct. A big price feels like the cheap bet. It costs very little, it might return a great deal, and if it loses, well, it was small. Measured over a very large number of runners, the long shots are where the charge is heaviest by a distance.

There is a reason a bookmaker can be generous with the favourite and hard with the outsider. Most money goes on the front of the market, so those prices have to stay competitive or punters go elsewhere. Very few people shop around for the best price on a 66/1 shot in a twenty-runner handicap, so nobody has to offer one.

None of that makes a long shot a bad bit of fun on National day. It does mean it is a worse bet than it looks, and that the two ends of the card are further apart than most people assume.

Tomorrow: how much of your stake the bookmaker keeps overall, worked in money rather than percentages.

Research, not tips. Every figure above describes what has already happened, not what will happen tomorrow.

Common questions

How do I turn odds into a percentage?

Divide one by the decimal price. From a fraction, add both numbers and divide the right one by the total.

Why do the percentages in a race add up to more than a whole?

Because the bookmaker's charge sits inside every price, and the excess is that charge. On the meetings we measured this summer it ran from 23.0% to 30.5% over a fair book.

Does a favourite winning about a third of the time mean the odds are wrong?

No. The favourite wins 35% across our sample, and short prices are close to accurate. The prices are good estimates. They are simply sold to you at a mark-up.

Are long shots ever worth backing?

Backing outsiders as a policy has returned -34.66% in our testing, and backing them each-way -30.28%. That does not mean a particular long shot cannot win. It means the price you get for one is, on average, the least generous on the card.

Is your model better at this than the market?

No. On accuracy scoring across 9,568 races our model reads 0.100 against the market's 0.091, where lower is better. The market wins, and we publish that because it is true.