The Islamic New Year (Arabic: رأس السنة الهجرية, Raʿs as-Sanah al-Hijrīyah), also called the Hijri New Year, is the day that marks the beginning of a new lunar Hijri year, and is the day on which the year count is incremented. The first day of the Islamic year is observed by most Muslims on the first day of the month of Muharram. The epoch (reference date) of the Islamic era was set as the year of the emigration of Muhammad and his followers from Mecca to Medina, known as the Hijrah, which equates to 622 CE in the Gregorian calendar.^[1] All religious duties, such as prayer, fasting in the month of Ramadan, and pilgrimage, and the dates of significant events, such as celebration of holy nights and festivals, are calculated according to the Islamic calendar.

While some Islamic organizations prefer determining the new month (and hence the new year) by local sightings of the moon,^[2] most Islamic institutions and countries, including Saudi Arabia,^[3] follow astronomical calculations to determine future dates of the Islamic calendar. There are various schemas for calculating the tabular Islamic calendar (i.e. not based on observation), which results in differences of typically one or even two days between countries using such schema and those that use actual lunar sightings. For example, the Umm al-Qura calendar used in Saudi Arabia was reformed several times in recent years. The current scheme was introduced in 1423 AH (15 March 2002).^[4]

A day in the Islamic calendar is defined as beginning at sunset. For example, 1 Muharram 1432 was defined to correspond to 7 or 8 December 2010 in civil calendars (depending on the country). For an observation-based calendar, a sighting of the new moon at sunset of 6 December would mean that 1 Muharram lasted from the moment of sunset of 6 December to the moment of sunset of 7 December, while in places where the new moon was not sighted on 6 December 1 Muharram would last from the moment of sunset of 7 December to the moment of sunset of 8 December.^[5]

Twelver Shia Muslims believe the Islamic new year is the first of Rabi' al-Awwal rather than Muharram, due to it being the month in which the Hijrah took place.^[6] This has led to difference regarding description of the years in which some events took place, such as the Muharram-occurring battle of Karbala, which Shias say took place in 60 AH, while Sunnis say it took place in 61 AH.^[7]

Since the Islamic lunar year is eleven to twelve days shorter than the solar year as approximated by the Gregorian calendar, the Islamic New Year does not occur on the same Gregorian calendar date every year.

The following dates are predicted for the Gregorian calendar dates to correspond with the Islamic new year, according to Saudi Arabia's Umm al-Qura calendar:^[8]

• Solar Hijri calendar#New Year's Day