You can usually feel a wrong favourite before the data tells you. The price drifts a tick. Then it pulls back in. Then someone hits the back side hard for a few hundred and the layers do not come back. Whatever the model said about that horse five minutes ago, the money no longer believes it.
That gap between the displayed price and what the money is doing is the seed of the disparity method. The question is where, on a real card, it is worth using.
Can you pick lay favourites using price disparity?
Not on its own. Across 13 years of GB and Irish racing the Betfair SP favourite wins 34.4% of the time at an A/E of 1.00 (actual wins divided by the wins the odds imply), so most favourites are priced about right. Disparity (the gap between a favourite’s price and its share of the traded money) is best treated as an experimental tiebreaker, used in the few conditions where favourites have run below par, after your own form read says the favourite is vulnerable.
What “laying” means
To lay a horse is to take the bookmaker’s side on one runner. You agree the price and accept the other person’s stake, and you pay out only if the horse wins. If it loses, finishes second or pulls up, you keep the stake.
One thing to know before anything else. Your risk on a lay bet is the liability, which is bigger than the stake. Lay a 4.0 shot for £10 and you stand to lose £30 if it wins. Size lay bets by liability, not by stake.
“Lay favourites” is shorthand for opposing the shortest-priced horse. It is not a strategy in itself. In our database of GB and Irish races from 1 July 2013 to 14 October 2026, the Betfair SP favourite won 34.4% of 167,257 races, with an A/E of 1.00 and a return of -1.4% to level stakes after 2% commission. An A/E of 1.00 means neither side has an edge, so laying every favourite blindly gets you nowhere.
So there is no blanket “lay every favourite” edge. There are conditions, and there are races. Finding them is the job, and our guide to laying the favourite covers the wider picture.
The disparity method in plain English
The method asks one question: does the money agree with the price on the favourite?
You are hunting for a false favourite. That is a horse at the front of the market whose form is weaker than a rival’s. False favourites usually appear because of a name, a recent headline or trainer fashion, rather than because the numbers justify the price. The disparity check looks for one clue in the live market: a favourite priced short that is not attracting the money you would expect at that price.
On Betfair, two numbers matter. One is the total matched on the whole event. The other is the amount traded on the favourite. Divide the favourite’s volume by the event volume to get its share of the money.
Now turn the displayed price into the share it implies. A price of 2.46 implies a share of about 41% (one divided by 2.46). Divide the money share by the price-implied share. That ratio is the disparity.
For example, if the favourite is 2.46 but has only taken 30% of the money, the disparity is 0.30 ÷ 0.41, about 0.74. The price says “strong favourite”, the money says “not that strong”.
The original idea was that a ratio at or below roughly 0.70, taken close to the off when the market has firmed up, was a flag worth respecting. A ratio of 1.0 or more means the money is backing the favourite at least as hard as its price implies, and that is not the one to oppose.
A caution on what this measures. Matched volume shows where money has traded. It is not the same as the true chance of winning, and it can also reflect liquidity and trading activity. That is why we call it an experimental measure.
The same volume numbers are available through Betfair’s exchange data feed and third-party tools. Do the check in the last few minutes before the off, because a market thirty minutes out is still half-formed.
What 13 years of favourites show
Before asking where disparity might help, here is the wider market. The splits in this section come from an earlier cut of the database, July 2013 to March 2026, with just over 162,000 favourites.
The favourite’s A/E is 1.00 and the win rate 34.4%. Slice by Betfair SP price band and the picture stays flat:
| Betfair SP band | Runners | A/E |
|---|---|---|
| Odds-on (1.5 or shorter) | just under 6,000 | 1.00 |
| 1.5 to 2.0 | over 17,000 | 0.99 |
| 2.0 to 3.0 | just under 50,000 | 0.99 |
| Above 5.0 | just over 19,000 | 0.99 |
Odds-on favourites in that group won 75.5% of the time. Every band lands within 0.01 of 1.00, so price level on its own is not a lay signal.
Race type tells the same story. Flat turf favourites run at A/E 0.99 across just under 60,000 starts, flat all-weather at 1.00 across just under 37,000. Chase and hurdle turf both land at 1.00. NH Flat is lowest at 0.97 across just under 6,000 favourites, but the gap is too small to lay on by itself.
The market is broadly right. If you want a lay-the-favourite read, you have to look harder than price level or race type.
Where favourites have underperformed
Two patterns showed up in this one historical cut. They are narrow and come from a single period.
Going. Soft to heavy ground has the favourite at A/E 0.91 across just over 2,000 runners, a 33.1% win rate. Underneath that, hurdle turf favourites on soft to heavy come in at 0.88 across 872 runners, and chase turf at 0.89 across 447. When the ground is bottomless and stamina becomes the main exam, the favourite may find it harder to answer. Heavy, yielding and good to soft on their own did not show the effect.
Field size. Across nearly 24,000 favourites in fields of 13 to 16 runners, A/E is 0.98 with a 27.0% win rate. That is a small shortfall on a big sample. Chase turf favourites in those fields run at 0.94 across 1,782 starts. NH Flat favourites in fields of 13 to 16 sit at 0.91 across 996. Flat all-weather favourites in big fields land at 0.97 across more than 5,500.
Class barely registers. Class 2 and Class 6 favourites both land at 0.99, and handicaps and non-handicaps at 1.00 and 0.99. The useful filter is field size, and the useful modifier is ground.
This is where a live-market check could earn a place. In a 16-runner hurdle on soft-to-heavy, you do not need a method to know the favourite is more fragile than usual. You need a way to see whether the money agrees on the day.
How to try it on today’s card
Treat disparity as the second filter, never the first.
- Filter by conditions. Start with soft-to-heavy ground, especially hurdle and chase turf, and fields of 13 or more, especially chase turf and NH Flat.
- Do your own form read. Use the ratings, the pace map and our betting systems guide to decide whether you think the favourite is weak. If your form read does not flag it, the disparity number is irrelevant.
- Check the disparity near the off. If the ratio is about 0.70 or lower, the favourite’s price is shorter than its share of the money would suggest. That is your extra flag.
Why trust it at all? Only because you can test it cheaply. Keep a simple log of every lay you consider in these conditions, and note whether the disparity flag was on or off. After a hundred or so, compare the two groups. If the flagged group is no better than the unflagged one, drop the check. If it is, you have found something worth a bigger sample.
Two bits of small print. Disparity on a market with low total matched is noisy, because one big bet can swing it. And track your results with A/E over a hundred bets or more, not a week. Lay bets win often and lose big, so a run of a few losers is normal. Keep liability per bet small enough that a bad week is easy to ride out.
The bottom line
The disparity method is a tiebreaker to test, not a system. The market gets favourites right nearly everywhere, the underperformance pockets are narrow, and the live price-versus-money check only earns its place after the form read and the conditions have done most of the work.
Framed that way, you spend less time hunting for false favourites everywhere, and more time spotting the handful of races a week where the favourite has real questions to answer.
Browse today’s race cards and look at the favourites in the big-field hurdles and chases. It is a good place to practise the form read before you ever lay a bet.
