Since 1966-2015
35% of Derby winners were born in January
23% in February
22% in March
13% in April
8% in May
The last 2 Derby winners Nyquist March and AP Feb

jbelfior: Conclusion?  More horses are born before April 1st?

Good Luck,
Joe B

johnnym: IWC is a May colt.

TheBull: McKracken is an April foal too, I believe

Molesap: I have similar data for a slightly different time period (which of course makes sense) with accompanying data on the percentage of thoroughbreds born in each month on average from 1975-2015. It seems there may be a maturity advantage with earlier born horses as over 50% of the winners of the Kentucky Derby have been born in January and February, but only about 20% of thoroughbreds overall were born in those two months. Here is the data:

34% of Derby winners were born in January (7% of thoroughbreds born in that month)
24% of Derby winners were born in February (14% of thoroughbreds born in that month)
22% of Derby winners were born in March (27% of thoroughbreds born in that month)
12% of Derby winners were born in April (31% of thoroughbreds born in that month)
8% of Derby winners were born in May (17% of thoroughbreds born in that month)
*Note the remaining 3% or so of thoroughbreds in general are born after May

johnnym: The Maturity angle was my thought on this since I do like IWC.

atakante: FWIW, Mohaymen last year was also a May foal.