Convert dates between Gregorian, Julian, Hebrew, Islamic (Hijri), Persian (Solar Hijri), Ethiopian, and ISO week date systems.
Solar calendar. 365.2425 days/year via leap year rule (Γ·4, except Γ·100, except Γ·400). Introduced 1582 by Pope Gregory XIII. Now the international civil standard.
Predecessor to Gregorian. Simpler leap year rule (every 4 years). Currently 13 days behind Gregorian (since 1900). Still used by some Orthodox churches for feast days.
Lunisolar calendar. Year AM 1 = 3761 BCE (traditional date of creation). 12β13 months per year. Months follow the moon; year follows the sun via intercalation. Used in Judaism for religious dates.
Purely lunar calendar. 354 days/year β about 11 days shorter than solar. No intercalation. Year 1 AH = 622 CE (Muhammad's migration to Medina). Religious dates cycle through all seasons over ~33 years.
Solar calendar used in Iran and Afghanistan. Year 1 = 622 CE (same epoch as Islamic). 365/366 days/year (more accurate than Gregorian). New year (Nowruz) at spring equinox.
Coptic-derived solar calendar. 13 months β twelve of 30 days, plus a 5β6 day 13th month (PagumΔ). About 7β8 years behind Gregorian. Ethiopian New Year in September.
International standard (ISO 8601). Week 1 = first week containing Thursday. Monday = day 1. Format: YYYY-Www-D. Used in business, manufacturing, and scheduling.
Astronomical counting system β continuous count of days since 1 January 4713 BC (Julian). Used in astronomy and software for calculating intervals between any two dates without calendar complications.