Yes, and the size of the effect is the surprising part.
Across 269 festival races this summer, the charge in races of sixteen runners or more came to nearly three times what it was in races of two to seven. That is not a modest drift, and it is the strongest single pattern in everything we have measured about betting markets. The table below has the figures.
It also has nothing to do with the quality of the horses or the prestige of the race. It is a consequence of how a book is built.
| Field size | Races | Runners | Overround | Takeout |
|---|---|---|---|---|
| 2 to 7 runners | 37 | 6.0 | 12.4% | 11.0% |
| 8 to 15 runners | 136 | 11.5 | 22.3% | 18.2% |
| 16 or more runners | 96 | 19.6 | 36.6% | 26.8% |
Pooled across 9 festivals, 269 races with a measurable book. Overround is the margin over a fair book; takeout is the share of stakes the book keeps.
Every race in that table had a full set of prices at the off, and the aggregation weights each band by how many races it holds, so the big-field row is not resting on a handful of outliers.
The mechanism is simple enough to check by hand. Price six runners and you make six judgements, each carrying a small charge. Price twenty-four and you make twenty-four, and the fifteen or so at the back of the market are the ones nobody scrutinises.
Long prices are where the fat sits. A 50/1 shot is marked as a one-in-fifty-one chance and, on our sample of 218,437 runners, horses at 50/1 and longer win about one time in a hundred and twenty-five. Every one of those in a big field adds to the total.
Small fields do not have room for that. With five runners the market is transparent, the money concentrates on two or three of them, and any firm out of line is obvious.
The big-field handicap is the race everyone talks about. It has the most runners, so it feels like the most opportunity, and there is a comfortable sense that with twenty horses in it, surely one of them is overpriced.
Some of them probably are. The catch is that you are being charged nearly three times as much for the chance to find one, and the extra charge lands whether you find one or not.
It is worth being precise about what this does and does not tell you. It does not say that small-field races are profitable. Our whole board of 24 tested approaches across 29,483 races has 0 in profit, and choosing cheaper races does not change that. It says the rate at which you lose is set largely by a number printed on the racecard before anyone has said a word about form.
For most people that is the more actionable fact, because you can read it at a glance and it does not require an opinion about a horse.
The two different percentages we keep quoting, and why they are not interchangeable, are laid out in overround and takeout.
None of these pages is a tip, and none describes a way to win. They describe what betting costs, which is a different and more reliable subject. If your betting has stopped being fun, BeGambleAware has free, confidential help, and the National Gambling Helpline is on 0808 8020 133.
Pooled across 269 festival races, the biggest fields carried close to three times the charge of the smallest. The table on this page gives the figures for each band.
Cheaper, not good. Every betting approach we have tested loses money, and betting in a cheaper race means losing more slowly rather than winning.
Each runner priced carries a slice of the charge, and long-priced runners carry the heaviest. A big field has many more of them, and they attract the least scrutiny.
No. These figures use the starting-price book on races with a full set of prices, so withdrawn horses are not counted in the field size.
We have only published the measurement for the 9 festivals we hold, which is 269 races. The mechanism is not festival-specific, but we would rather show you the data we have than assert the rest.
Every figure here is pulled live from our data and nothing beats the bookmaker's margin. For whether anyone holds a real edge, see our track record. 18+, please bet responsibly.