Solar Hijri calendar

The Solar Hijri calendar is the official calendar of Iran and the most widely used calendar in Afghanistan. It is a solar calendar, based on the Earth's orbit around the Sun. Each year begins on the day of the March equinox and has years of 365 or 366 days. It is sometimes also called the Shamsi calendar, Khorshidi calendar, Persian calendar, or Iranian Solar calendar and the most recent of the Iranian calendars. It is abbreviated as SH, HS, AP, or, sometimes as AHSh, while the lunar Hijri calendar (commonly known in the West as the 'Islamic calendar') is usually abbreviated as AH.

The epoch (very first day of the first year) of the Solar Hijri calendar was the day of the spring equinox, March 19, 622 CE. The calendar is a "Hijri calendar" because that was the year that Muhammad is believed to have left from Mecca to Medina; this event is referred to as the Hijrah.

The calendar is widely used by many Central Asian and West Asian ethnic groups, such as the Kurds, Pashtuns, Tajiks, Hazaras, Persians, Azerbaijanis, Yazidis, Lurs, Gilaks, Mazanderanis, Qashqais, Khorasani Turks, Nuristanis, Pashayis, Aimaqs, and Talysh people. Smaller groups of Turkmens, Balochs, Uzbeks, and Arabs also use this calendar.

Since the calendar uses astronomical observations and calculations for determining the vernal equinox, it theoretically has no intrinsic error in matching the vernal equinox year. According to Iranian studies, it is older than the lunar Hijri calendar used by the majority of Muslims (known in the West as the Islamic calendar); though they both count from the year of the Hijrah. The solar Hijri calendar uses solar years and is calculated based on the "year of the Hijrah," and the lunar Hijri calendar is based on lunar months, and dates from the presumed actual "day of the Hijrah".