World calendar converter

The world does not all live by the same date scale. The Gregorian calendar, used today in most countries for civil purposes, was adopted only gradually over the centuries and remains offset from religious, cultural or historical calendars. Converting a date helps understand a festival, read an ancient document, coordinate an international event or simply satisfy historical curiosity.

This calendar converter covers several major systems: the Gregorian calendar, the Julian calendar that preceded it, the Islamic (Hijri) calendar based on lunar cycles, the Hebrew calendar used for Jewish festivals, the traditional Chinese calendar, the Persian (Iranian) calendar and the Indian civil calendar. You enter a date in one of these systems and the tool displays the equivalents in the others.

The Gregorian calendar is the international civil system. It counts 365 days, plus a leap day every four years with a few secular exceptions. The Julian calendar, introduced by Julius Caesar in 46 BC, is similar but treats too many years as leap years: it gradually drifted by 10 to 13 days depending on the country, which explains differences with ancient documents.

The Islamic or Hijri calendar is a pure lunar calendar. Each month begins with the new moon, and a year has 12 months of about 354 days. Islamic festivals such as Ramadan or Eid therefore shift back by about eleven days each Gregorian year. The Hebrew calendar is lunisolar: it follows lunar cycles for months, but adds intercalary months to stay aligned with the seasons, which allows Passover to remain in spring.

The traditional Chinese calendar is also lunisolar and associates each year with a zodiac animal. The Persian, or Iranian, calendar is a very precise solar calendar with years beginning at Nowruz and a leap-year rule based on 33-year cycles. The Indian civil calendar, used for administration in India, is solar and generally begins the year on 22 or 23 March.

Historians and genealogists use the Julian/Gregorian conversion to interpret old records: a birth recorded as 15 February 1700 in Julian Russia actually corresponds to 26 February Gregorian. Travellers and expatriates consult the Islamic calendar to know Ramadan dates in their host country. Jewish communities convert Hebrew dates to celebrate Hanukkah, Purim or Passover on the correct civil date.

In international business, a contract drawn up under the Persian or Chinese calendar benefits from conversion so all parties understand it. Teachers and students of religious history, diplomatics or oriental studies use these equivalences regularly. The tool gives a reliable approximation; for liturgical or legal uses, it is still advisable to check with a local authority or official almanac.