The Shamsi Calendar, also known as the Persian Calendar or Solar Hijri Calendar, is a solar calendar used primarily in Iran and Afghanistan. It is based on the Earth's revolutions around the Sun, consisting of 12 months that total 365 days in a common year and 366 days in a leap year. The calendar begins with the vernal equinox, marking the start of spring. Each month in the Shamsi Calendar has either 30 or 31 days, with the first six months having 31 days and the next five having 30 days. The final month, Esfand, has 29 days in a common year and 30 days in a leap year. This calendar is widely used for civil purposes and is recognized for its accuracy in tracking the seasons.