Irish vs UK racing: is one market dearer? We measured the overround in 188,740 races

The short answer: Irish starting prices are noticeably more expensive than British ones. Across 188,740 races the average British SP market carries about 15.8% margin. The Irish figure is about 24.6%. That gap is real, it is not just because Ireland runs bigger fields, and it is the single clearest thing that separates the two markets.

The Overlay strips the bookmakers' margin out of a market to show every runner's fair odds, so the size of that margin is our bread and butter. A natural question: is the margin the same wherever you bet? We took every UK and Irish race in our database from 2010 to 2026 that settled with a full starting-price book, worked out the overround on each one, and split it by country. Here is what nearly 1.8 million priced runners say.

What the overround is, and why it matters

Every price implies a chance. Evens is 50%, 4/1 is 20%, and so on. Add up the implied chance of every runner in a fair race and it comes to 100%. In a real book it comes to more than 100%, and the excess is the overround: the margin the layer builds in. A 20% overround means the book adds up to 120%, and that extra 20 points is, on average, what the market charges you to play.

You can see the same thing in the results. Add up every runner's SP-implied chance across all our races and you get far more "winners" than actually occur: about 15% too many in Britain, about 24% too many in Ireland. The surplus is the margin, and it lands in the same place both times, just deeper in Ireland.

Like for like, Ireland is dearer at every field size

Irish fields are bigger on average (about 11.7 runners against 9.1 in Britain), and overround climbs steeply as fields grow, so some of the headline gap is simply down to Ireland running more big-field races. But it is not all of it. Match the two markets field size for field size and Ireland is still dearer in every band, and the gap gets wider the bigger the field.

So field size explains part of the raw difference, but a like-for-like Irish race still carries more margin than its British equivalent, and in a big-field Irish handicap the overround can push towards 40%. The lesson is the ordinary one: the more runners, the fatter the book, and Ireland starts from a higher base.

Flat or jumps, the pattern holds

Splitting by code tells the same story. British flat and jumps markets are priced at a similar margin to each other, and both are tighter than anything in Ireland, where flat and jumps are both close to a quarter.

What it costs if you just back everything

The margin is the market's price. The actual damage to a blind backer is a little worse again, because staking the same on every runner puts too much on the longshots, and longshots lose more than their price suggests (our favourite-longshot bias piece has the detail). Back every runner to level stakes at SP and the numbers look like this.

Neither is a strategy, and neither is meant to be. The point is the direction and the size of the gap: whatever you do at random, it costs you more in Ireland.

One thing that is not different: the favourite

It would be easy to read all this as "Irish prices are bad", but that is too broad. The favourite, the sharpest price in any race, is priced almost as tightly in Ireland as in Britain, which is why our separate study of favourites in Britain and Ireland found the two so close. The extra Irish margin does not sit on the favourite. It sits across the rest of the field, on the mid-priced and longer runners, where there is more room to load the book. If you only ever played short-priced favourites you would barely notice the difference. The further out you look, the more it bites.

Method, in plain English

We used every UK and Irish race in our database from 1 January 2010 to 2 November 2026. A runner is counted if it went to post and returned a starting price, fallers and pulled-up horses included (they still carried a price). The overround on a race is the sum of every runner's SP-implied chance minus 100%, measured only on the 188,740 races where the full field had a starting price (Britain 148,597, Ireland 40,143). A/E is winners divided by the winners the SPs implied. ROI is level-stakes return at SP: one point on every runner. Country is as recorded against the meeting (meetings without a country are left out of the comparison). Figures are historical, cover starting prices only (not early prices or the exchanges), and are for information, not a guarantee of anything.