Egypt's Dar al-Iftaa answers readers' questions in various fatwas. We at See publish these fatwas. The question says:
I wanted to know if it is possible to fast during Ramadan while you are on your period. I know that travellers and those sick (along side girls on periods) can be exempted from fasting, however if they are able to fast they can. It makes sense and wanted to know if that applies on those that have a menstrual cycle, especially if they want to fast and are able to (only they know their strength.)
It is impermissible for menstruating women or those in post natal bleeding to fast. The issue of menstruation and post natal bleeding differs from the fast of the sick and travelers. Breaking the fast on account of sickness and travel is a legal dispensation, while it is obligatory for women in menses and post natal bleeding to refrain from fasting.