A Hebrew birthday (also known as a Jewish birthday) is the date on which a person is born according to the Hebrew calendar. This is important for Jews, particularly when calculating the correct date for day of birth, day of death, a bar mitzva or a bat mitzva. This is because the Jewish calendar differs from the secular and Christian Gregorian calendar as well as from the Islamic calendar, in most years the two birthdays do not coincide - typically, they coincide just once in 19 years.