Is the Kentucky Oaks more predictable than the Kentucky Derby?

The Kentucky Derby (G1) at Churchill Downs is the most famous race in North America. Its companion race, the Kentucky Oaks (G1) for fillies, is a prestigious prize in its own right.

Every year, the two races draw intense scrutiny from bettors, especially the Derby. With a maximum field of 20 horses (highly unusual in North America), the Kentucky Derby is a handicapping challenge unlike any other.

It stands to reason that the Kentucky Oaks, which is limited to 14 starters, is an easier race to handicap. Smaller fields feature fewer possible outcomes and generally yield more predictable results.

But do the facts line up with expectations? A statistical analysis can tell us whether picking the Kentucky Oaks winner is indeed easier than picking the Kentucky Derby winner.

Defining actual field sizes and win probabilities

First, let’s review Kentucky Derby and Kentucky Oaks field sizes from the past 20 years. Just because the races can feature a maximum of 20 and 14 starters doesn’t mean they draw full fields every year.

Here are the field sizes for the two races from 2005-2024:

While the Kentucky Oaks featured full fields in 12 of the last 20 editions, a few smaller fields (including two with only seven starters) brought the average number of starters down to 12.45. If every horse were perceived to have an equal chance at winning, we would expect the average odds for a Kentucky Oaks winner to be approximately 11.45-1.

The Kentucky Derby featured a full 20-horse field in 11 of the last 20 years. The average number of starters was 19.25, so all else being equal we would expect the average Kentucky Derby winner to start at 18.25-1.

Actual average odds for Kentucky Derby and Oaks winners

In reality, it’s impossible to assemble a group of Kentucky Derby or Oaks starters who are perfectly matched. There will always be some with higher speed figures and better credentials than others, so the faster and more accomplished horses start at lower odds and have a better chance at winning than unheralded longshots.

In a small field, there’s less chance of chaos and troubled trips affecting the outcome. The pace is more likely to be typical than extreme. These factors, in theory, should increase the likelihood of a well-regarded horse visiting the winner’s circle.

This is reflected in the average odds of Kentucky Derby and Kentucky Oaks winners from 2005-2024:

The average Kentucky Oaks winner started at about 9.54-1, a couple of ticks lower than the 11.45-1 odds we might expect for the average field size. In contrast, the average Kentucky Derby winner started at odds nearly twice as high: 18.98-1, pretty much in line with the 18.25-1 odds expected for the average field size.

Median odds of Derby and Oaks winners paint a similar picture

Average odds can be thrown off by extreme outcomes, such as the 80.80-1 upset of Rich Strike in the 2022 Kentucky Derby or the 47.10-1 surprise of Lemons Forever in the 2006 Kentucky Oaks. That’s where median winning odds can give us a different perspective.

Below are the odds for every Oaks and Derby winner from 2005-2024, sorted from lowest to highest. At the bottom are the median winning odds:

From 2005-2024, the median winning odds of Kentucky Oaks winners came in at 4.65-1, which means 10 winners started at higher than 4.65-1 and 10 winners started at lower than 4.65-1.

In contrast, the Kentucky Derby yielded median winning odds of 8.20-1, not quite twice as high as in the Oaks. Nine of the 20 Derby winners during the 2005-2024 timeframe started at double-digit odds, compared to six Oaks winners starting at double-digit odds.

Highest and lowest winning odds concur

The highest and lowest winning odds in our 20-year sample size tell pretty much the same story. The lowest-priced Kentucky Derby winner was Nyquist, who closed at 2.30-1 in 2016. On the other hand, four Kentucky Oaks winners started at odds between 0.30-1 and 1.50-1.

At the other end of the spectrum, the highest-priced Kentucky Oaks winner in the last 20 years (and, actually, in the race’s entire 150-year history) was Lemons Forever at 47.10-1 in 2006. Yet we’ve seen four Kentucky Derby winners during the same timeframe start at odds between 50.30-1 and 80.80-1. The 80.80-1 upset of Rich Strike was the second-biggest in history behind Donerail (91.45-1 in 1913).

Tally of winning favorites provides an opposing data point

By one metric, the Kentucky Derby has been more predictable than the Oaks. The favorite has won eight of the last 20 editions of the Derby (40%), while only six Oaks favorites (30%) have prevailed during the same timeframe.

There is, however, a key difference. In eight of the 14 years (57%) in which the Oaks favorite was beaten, the winner was a filly starting at single-digit odds. In contrast, when Derby favorites fell to defeat, the winner started at single-digit odds in only three of the 12 years (25%).

Conclusions

Overall, the data is clear. Based on winning odds, from 2005 through 2024 the Kentucky Oaks was a more predictable race than the Kentucky Derby, and by more than we might expect.

Even though the average Kentucky Derby field size is only 54.6% larger than that of the Kentucky Oaks, the Derby produces average winning odds 99% higher than in the Oaks, and median winning odds 76.4% higher. These increases are driven from both ends of the odds spectrum: by more frequent and larger upsets, and by fewer short-priced winners.

If you’re looking for a longshot winner during Derby and Oaks week, focus your attention on the Derby, which is more likely to produce a double-digit winner. If you want to simplify and bet only a few short-priced horses (perhaps in a multi-race wager), the Kentucky Oaks—with its smaller and more predictable field—is the race for you.