How the Afghan Calendar Works
A technical and historical overview of the Solar Hijri (Shamsi) system.
Astronomical Logic
The Afghan calendar is **strictly astronomical**. While the Gregorian calendar uses mathematical approximations (adding a leap day every 4 years), the Shamsi calendar determines the start of the year based on the exact moment of the **Vernal Equinox**.
This moment, known as *Tahwil-e Sal*, is when the center of the Sun crosses the celestial equator. If this happens before noon in Kabul, that day is the first of Hamal. If it happens after noon, the next day is the first of the year.
Month Durations
The 12 months are divided into three groups:
- Months 1-6 (Hamal to Sunbula): Always 31 days long. These correspond to the Spring and Summer seasons.
- Months 7-11 (Mizan to Dalwa): Always 30 days long. These correspond to Autumn and the start of Winter.
- Month 12 (Hut): Usually 29 days, but 30 days in leap years.
Historical Context
The Solar Hijri calendar was officially adopted in Afghanistan in **1922** during the reign of King Amanullah Khan. Before this, the Lunar Hijri calendar was the primary system for all government and social affairs.
The adoption of the Shamsi system allowed for a more consistent agricultural and taxation cycle, as the months became fixed to the solar seasons.
Leap Year Calculation
Because it is an observation-based calendar, leap years do not follow a simple "every 4 years" rule. Instead, they occur in cycles of 33 years (and sometimes others). This makes the Afghan calendar much more accurate than the Gregorian system, with an error of only one day every **110,000 years**.