Key points
- The Dosage Index (DI) is a pedigree-based number that compares speed-leaning and stamina-leaning influences in a Thoroughbred's first four generations.
- It measures inherited tendency, not ability or class.
- Chef-de-race ancestors earn 16, 8, 4 and 2 points by generation, and those points feed the formula.
- A higher DI points to a more speed-oriented pedigree. A lower DI points to a more stamina-oriented one.
- The 4.00 Kentucky Derby threshold is a historical convention, and several Derby winners broke it.
- Treat the index as background on distance aptitude, and weight the race itself more heavily.
What is a dosage index in horse racing?
A dosage index is a number derived from a Thoroughbred's pedigree. It compares speed-leaning and stamina-leaning influences in the first four generations of the family tree. Handicappers quote it most often when they discuss whether a horse can handle the Kentucky Derby's distance.
The number describes inherited tendency. It says nothing direct about how fast a horse is or how good it is. The index is still quoted today, but many handicappers treat it as a loose guideline.
Where the dosage index comes from
Three people built the idea in stages. J.J. Vuillier proposed the concept of chefs-de-race, which are influential sires whose offspring shaped the breed. A chef-de-race is a stallion whose influence on speed or stamina was strong enough to earn a place on a reference list.
Franco Varola then sorted these sires into five aptitude categories:
- Brilliant: sprint speed.
- Intermediate: speed that carries a little farther.
- Classic: balanced speed and stamina.
- Solid: stamina-leaning.
- Professional: extreme stamina.
Steven Roman added a four-generation point system and the index itself in the late 1970s. Roman revises his chef-de-race list over time, so check the current version before you rely on any count of how many sires it holds. Roman and Alan Porter also wrote a free report on the practical use of dosage and nicking, published by BloodHorse.
How the dosage index is calculated
Each chef-de-race in a horse's first four generations earns points based on its position in the pedigree. According to the Werk Thoroughbred Consultants FAQ, the points are:
- 16 for the sire (first generation).
- 8 for each ancestor in the second generation.
- 4 for each ancestor in the third generation.
- 2 for each ancestor in the fourth generation.
A chef-de-race splits its points across the categories assigned to it. Add up the points in each category, then apply this formula:
DI = (Brilliant + Intermediate + (Classic ÷ 2)) ÷ ((Classic ÷ 2) + Solid + Professional)
Grouping matters here. The top and bottom of the fraction each get calculated in full before you divide.
A worked example
This pedigree is illustrative only. It does not describe a real horse, and the category assignments are invented to show the arithmetic.
Suppose a horse has three chefs-de-race:
- The sire (16 points) is assigned half to Brilliant and half to Classic. That gives 8 to Brilliant and 8 to Classic.
- A second-generation ancestor (8 points) is assigned entirely to Solid. That gives 8 to Solid.
- A third-generation ancestor (4 points) is assigned entirely to Intermediate. That gives 4 to Intermediate.
The totals are Brilliant 8, Intermediate 4, Classic 8, Solid 8 and Professional 0.
The top of the fraction is 8 + 4 + (8 ÷ 2) = 16. The bottom is (8 ÷ 2) + 8 + 0 = 12. The DI is 16 ÷ 12, or 1.33.
Center of Distribution
The Center of Distribution (CD) is the companion figure. It works as a balance point, with values typically falling between about +2 and -2. Positive values lean toward speed, and negative values lean toward stamina.
Finding a horse's dosage profile
A lookup needs two things: the horse's pedigree and the current chef-de-race list. Published dosage profiles appear in pedigree and sales references that report the index and CD for each horse. Because the values are already published, you rarely need a standalone calculator. The worked example above lets you check any figure you see.
How to read the number
Direction comes first. A higher DI means a more speed-oriented pedigree, and a lower DI means a more stamina-oriented one. A value near 2.00 suggests a pedigree with a fairly even mix, while a value above 5.00 suggests a strong lean toward speed. Band labels such as "professional" or "brilliant" vary by source. They are handicapping conventions, not official classifications.
The best-known cutoff is 4.00 for the Kentucky Derby. The race runs 1¼ miles, a distance that made stamina the focus of pedigree discussion, and horses with a DI above 4.00 were often doubted. That threshold is a historical convention. It is not a rule of the sport.
Does the dosage index still work?
The record shows the threshold has failed. The Werk Thoroughbred Consultants FAQ lists Derby winners that broke 4.00: Strike the Gold (9.00) in 1991, Real Quiet (5.29) in 1998, Charismatic (5.22) in 1999 and Giacomo (4.33) in 2005. Check the figures for later winners against a primary source before drawing conclusions about recent years.
The index was built to gauge distance aptitude. It was not designed to pick winners or to plan matings. The consultant view in the Werk FAQ is that breeders should use it only to balance speed and stamina in a mating. A high-DI horse can win a route race, and a low-DI horse is not automatically a good distance horse.
EquinEdge takes the same stance toward all pedigree numbers: they are inputs that inform judgment, and they do not replace it.
Using the dosage index alongside other handicapping tools
The Dosage Index describes inherited tendency. Speed figures and pace describe what a horse has already done. A handicapper can read the two together: a horse with a speed-leaning DI that has posted strong figures at a route distance has evidence on both sides, while a stamina-leaning pedigree with weak figures needs a better reason to be backed. Running style, surface preference and sire distance records round out the picture. All of it sits inside the wider process of horse racing handicapping.
For readers who want a pedigree measure built for current use, EquinEdge's Genetic Strength Rating (GSR®) uses pedigree and performance to evaluate a horse's suitability for a race's distance and surface. You can see it inside EquinEdge's AI-powered handicapping tools with a free trial.
Treat the dosage index as background on distance aptitude, and give the race itself more weight.
FAQ
Is a high or low dosage index better?
Neither is better. A high DI points to a speed-leaning pedigree and a low DI to a stamina-leaning one. Which suits a horse depends on the race distance and what the horse has shown on the track.
Can I use the dosage index to plan a breeding?
The index was not designed for that. The Werk Thoroughbred Consultants view is that breeders should use it only to balance speed and stamina in a mating.
Where can I find a horse's dosage index for free?
Look for published dosage profiles in pedigree references, which list the DI and CD for each horse. If you want to verify a number, you need the horse's pedigree and the current chef-de-race list, then apply the formula above.