A Pennsylvania study found that more than 80% of adult does are bred during a 6-week period from late October through the first week of December, with most of them conceiving in mid-November.
From conception date, the whitetail deer has a gestation period of 200 days.
Fast forward to the next spring and do the math. According to my calculations, in regions where the deer breeding season occurs from late October through early December (most of the country), more than 80% of fawns will be born from approximately May 12 through June 25, with the vast majority of little deer being dropped from May 29 through June 10, give or take a few days.
In late May and early June, there is plenty of food in the woods, which allows does and fawns to pack on pounds quickly. After 10 weeks, fawns are responsible for feeding themselves.
The Pennsylvania researchers point out that in an area with a late October to mid-December breeding season, the probability of a fawn being born after August 2 is 2%; after August 13 it drops to 1%. Two of every 100 fawns were conceived very late and are born very late the following summer.