When do people celebrate virgin Mary's birthday?

The Catholic Church celebrates the conception of Mary in her mother's womb on the Feast of the Immaculate Conception, December 8. This is a solemnity (Holy Day of Obligation) and all Catholics past the age of reason are bound to attend Mass on this day. Her birthday is then celebrated exactly nine months later, on September 8.

If you wanted to do something special for Mary on this day, besides attending Mass, it would be especially fitting to pray a rosary or place flowers before her statue at a church.

In Medjugorje, where the Virgin Mary has been appearing since 1981, she has told the visionaries that her real birthday is August 5. She also asked them as a special tribute to this date, they should fast for two days and then celebrate. So if you believe in the messages given at Medjugorie, you could also do that around August 5.