Do all countries use the same calendar?

The Gregorian calendar is the internationally accepted civil calendar. It was introduced by Pope Gregory XIII.

But there are other types of unofficial calenders used by some groups of people around the world.

* Calenders have public/bank/mercantile holidays marked on them specific to that country.

* In Sri Lanka, calendars have Full moon days marked on them, because Full moon days are public holidays.

* Chinese calendar is a lunisolar calendar, incorporating elements of a lunar calendar with those of a solar calendar.

* Islamic (Muslim/Hijri) calendar is a lunar calendar, used to date events in Muslim countries, by Muslims to determine the days to celebrate Islamic holy days and festivals.

no,. because in my country there are lot of islands and its used a different calender from each island to the other islands