Calendar Converter

The Gregorian calendar, introduced by Pope Gregory XIII in 1582, corrects the Julian calendar by skipping 3 leap years every 400 years. The Julian calendar, established by Julius Caesar in 46 BC, adds a leap year every 4 years without exception, making it slightly too long. As of 2026, the Julian calendar is 13 days behind the Gregorian. Most of the world switched to Gregorian by the 20th century; Russia switched in 1918, Greece in 1923.

Orthodox churches that follow the Julian calendar (Russian, Serbian, Georgian Orthodox) celebrate Christmas on December 25 Julian, which falls on January 7 Gregorian. Churches that use the Revised Julian Calendar (Greek, Romanian, Bulgarian Orthodox) celebrate on December 25 Gregorian (same as Western Christmas). The difference comes from the 13-day gap between Julian and Gregorian calendars accumulated since the Council of Nicaea (325 AD).

The Islamic calendar is a purely lunar calendar of 12 months, each beginning with the new moon crescent. A lunar year is about 354 days (11 days shorter than the solar year), so Islamic dates shift approximately 11 days earlier each Gregorian year. This is why Ramadan and Eid move through all seasons. Year 1 AH (Anno Hegirae) corresponds to 622 CE, the year of Muhammad's migration from Mecca to Medina.

The Hebrew calendar is a lunisolar calendar: it tracks lunar months but adds a 13th leap month (Adar II) 7 times in every 19-year cycle (Metonic cycle) to stay aligned with the solar year. Year 1 AM (Anno Mundi) corresponds to 3761 BCE in the traditional Jewish reckoning of creation. The Hebrew calendar governs Jewish religious holidays: Rosh Hashanah, Yom Kippur, Passover, etc.

The Maya Long Count is a vigesimal (base-20) positional calendar counting days from the mythical Maya creation date (August 11, 3114 BCE in the proleptic Gregorian calendar). It uses five units: Baktun (144,000 days), Katun (7,200 days), Tun (360 days), Uinal (20 days), Kin (1 day). The famously misinterpreted "end date" of December 21, 2012 was simply the rollover from 13.0.0.0.0 to 14.0.0.0.0 (or 0.0.0.0.0 depending on interpretation), similar to a car odometer resetting.

The Solar Hijri calendar (also called the Iranian or Jalali calendar) is the official calendar of Iran and Afghanistan. It is a solar calendar starting from the Hijra (622 CE) but using solar year length. The year begins at Nowruz (Persian New Year) on the spring equinox, around March 20–21 Gregorian. It is extremely accurate — more precise than the Gregorian calendar. The current year is 1404 SH (2025–2026 CE).

The Ethiopian calendar (Ge'ez calendar) is based on the Coptic calendar, which is derived from the ancient Egyptian calendar. It has 13 months: 12 months of 30 days and 1 intercalary month (Pagume) of 5 or 6 days. Ethiopia is approximately 7–8 years behind the Gregorian calendar (they celebrated the new millennium in 2007). Ethiopia uses its own year count, currently approximately in the year 2017 ET.

The Byzantine calendar (also called the Creation Era or Anno Mundi) was used by the Eastern Roman (Byzantine) Empire and Orthodox Churches until the 18th century. Year 1 AM is September 1, 5509 BC, based on the Byzantine reckoning of the world's creation. The Byzantine New Year begins on September 1. Russia used this calendar until 1700, when Peter the Great switched to the Julian calendar (and later the Soviet Union switched to Gregorian in 1918).

The Coptic calendar is used by the Coptic Orthodox Church of Egypt. It has 13 months (12 of 30 days, 1 of 5–6 days) and is derived from the ancient Egyptian calendar. Year 1 AM in the Coptic calendar corresponds to 284 CE (the accession of Emperor Diocletian, who persecuted Christians — called the "Era of Martyrs"). The Coptic calendar year is currently approximately 1741 AM. Easter and Coptic feasts are calculated in this system.

The Gregorian calendar is very accurate but not perfect. It has a year of 365.2425 days, compared to the solar year of 365.24219 days. The error is about 1 day every 3,300 years. The Gregorian reform in 1582 also corrected the accumulated 10-day error from centuries of Julian use by skipping October 5–14, 1582. The Persian Solar Hijri calendar is even more accurate, with an error of about 1 day every 141,000 years, achieved through a more complex leap year rule.