Sefer Ha’mitzvos Ha’Katzar (The concise book of mitzvos)
By the Chofetz Chaim
This book lists the Torah mitzvos that can be observed today
First Section – the Positive Commandments
32. It is a positive commandment to fast on Yom Kippur
As it states in Vayikra (Leviticus) 23:27: "Also, on the tenth day of the seventh month... you shall afflict your soul." One is required to fast from evening to evening and one should add from the weekday onto the Holy day. Anyone that adds to his meals on the day before Yom Kippur is as if he fasted on the ninth and the tenth (see the Negative commandments, 152).
This applies in all places and at all times, for men and for women.