The Mathematical Basis for Successful Overlay Wagering
If luck were all, you wouldn’t need help in overcoming the odds in horse race pari-mutuel wagering.
You could bet your lucky number, and still have as much chance as a spin of the roulette wheel, or the throw of the dice.
But, in fact, unlike games of pure chance, horse race handicapping is a competition among players skilled in the knowledge of how and why some horses win races, and others do not. If it were not a game of skill, why does the favorite win more often than the second favorite, and the second favorite win more often than the third favorite, and so on?
It’s because the win pools, and therefore the betting favorites, are controlled, as if by an “invisible hand”, to reflect each horse’s chance of winning. The collective wisdom of all the individual players is somehow, when added together, able to sift and weigh all the intangible and conflicting factors: the best jockey is not on the best horse, the best horse is not in top condition, the horse coming up to its best race is “parked” on the outside in a large field; or “buried” on the rail. All of these contradictory factors are analyzed and reflected in the win pools, and in the resulting odds that emerge as the horses approach the starting gate. Amazingly, if we adjust for the track take-out, the final tote odds mirror the true, underlying, probabilities of each horse’s chance of winning, with few exceptions.
In order to win, you must find the exceptions. You must hunt for “overlays”. For only when you find an overlay, is there a chance to profit. An overlay is defined as a horse whose true chance of winning is better than that reflected in the tote odds. An overlay occurs when the public overlooks something. It could be a missed workout, a significant jockey change, a trainer angle, or, more likely, a critical combination of several factors.
Finding such a horse with an overlay to its true odds is the great challenge in horse race handicapping, but it is the only way to profit at the races.
If all of the money wagered in the win pool was returned to the betting public, at least the pari-mutuel odds would approximate “fair odds”, and one could hope to break-even. That is, a horse with a 33% chance to win would offer odds of 2/1. [(1/Win%) -1], or [(1/0.33) -1] = 2. However, because of the “take-out” (necessary to cover operating expenses, purses, and taxes), only some 78% of the pot is typically distributed, and that means the average bettor loses 22% of his investment (ROI = – 22%). In this example, a horse with one-third the money placed on it (our 33% implied win percentage) would actually show about 7/5 on the board.[(1-TakeOut/Win%) -1], or [(1-0.22/0.33) -1] = 1.36 (which is about 7/5). This makes the discovery of overlays even more critical if one hopes to pull ahead of the game.
Because of the take-out, pari-mutuel wagering is a negative sum game, and, therefore, track odds for most contenders are underlays. Serious contenders, whose strengths are usually obvious, are often over-bet, and normally do not offer good value. It is not enough to know which horses have a good chance to win. You must know precisely the win probability in order to calculate the fair odds for each contender. The best horse may not be the best bet. You must hunt for the contender whose chance of winning is better than the tote odds imply. Often, the second or third ranked contender is the value bet.
By definition, underlays lead to losses because the pay-off is not enough to overcome the losing events, and overlays lead to profits because the payoff is more than enough. A horse with a win probability of 50% paying $5.00 has an ROI of + 25%. That is, win every other wager, and collect $1.00 profit on a $4.00 investment. Betting such horses will build a steady profit.
It is foolish to attempt to win at the racetrack without the support of a serious odds line. A successful horseplayer must force himself to evaluate the “relative” chances of the contenders in order to discover the value bet, if any. They must, in turn, assign probabilities to each of these contenders and convert these to odds. For example, if you think a horse has a 25% chance of winning, you must command better than 3/1 to justify the wager. This is a tough process, but it must be done. Many handicappers examine the “raw” running lines to accomplish that. Other more sophisticated players will additionally consider pedigree stats, enhanced jockey and trainer stats or other generally enhanced data from companies like TrackMaster. Of course many will combine these with a physical examination of the horses just before the race.
However you do it, the key is to force yourself to construct an odds line.