There have been a number of threads that discussed this question. If you search for them, you will find many answers different than mine.
Depending upon the fragrance, it takes me about 22 - 28 sprays to fill a 2ml atomizer. If I assume 25 sprays equals 2ml then 100ml equals 1,250 sprays. If I use four sprays per day, a 100ml bottle should last about 312 days.