What calendar is the birthday calculated according to?

For example, today is 20 1 1, 1, and this is the Gregorian calendar, that is, Lunar New Year's Eve is 12, that is, Lunar New Year's Day is 1, that is, the lunar calendar is a global date, and the Gregorian calendar is only the date on our China website and ID card. Everyone should fill in the lunar calendar, and birthdays and constellations should also be counted according to the lunar calendar. It's just the tradition of some old people in China, so the older generation will calculate according to the solar calendar.