Everyday world · Updated September 2026
Calendar systems of the world
Most of the world uses the Gregorian calendar for civil dates. Islamic, Hebrew, Chinese and Indian calendars still set holidays. Leap years and why 1582 matters.
A calendar is a rule for naming days. The civil calendar in most countries is the Gregorian calendar, introduced in 1582 to fix drift in the older Julian calendar. English-speaking countries adopted it later (Britain and its colonies in 1752).
Religious and cultural calendars still run in parallel. The Islamic (Hijri) calendar is lunar — dates slide through the solar year. The Hebrew calendar is lunisolar. China and many in East Asia use a lunisolar calendar for festivals. India uses several, including Vikram Samvat and the National Calendar (Saka) for some official purposes.
Leap years add 29 February. The Gregorian rule: a year is a leap year if divisible by 4, except century years, which must be divisible by 400. So 2000 was a leap year; 1900 was not; 2100 will not be.
Calendar systems of the world — key facts (2026)
| Topic | Fact |
|---|---|
| Global civil default | Gregorian |
| Gregorian start | 1582 (Catholic states); UK 1752 |
| Leap-day month | February 29 |
| Islamic calendar | Lunar — Ramadan moves each year |
| Hebrew calendar | Lunisolar |
| Chinese New Year | Lunisolar — late January or February |
| India (examples) | Saka (national), Vikram Samvat, regional calendars |
| ISO date | YYYY-MM-DD (ISO 8601) |
Figures are the usual classroom and news-desk numbers for 2026. Border disputes and membership votes can change a count by one or two.
People also ask
What calendar does the world use?
Gregorian for business, visas and most governments. Holidays may follow another calendar.
Why does Ramadan move?
The Islamic year is about 11 days shorter than the solar year, so the month walks through the seasons.
Was 2000 a leap year?
Yes. Century years leap only if divisible by 400.