In the Solar Hijri calendar, Nowruz falls on the first day of Farvardin, the first Persian month.
Farvardin begins the Iranian solar year and corresponds to the arrival of spring in the Northern Hemisphere. Unlike a fixed Gregorian date, Nowruz is determined by the March equinox. In Iran’s calendar system, the precise timing of the equinox helps determine whether Nowruz begins on the same civil day or the following day.
The Solar Hijri calendar is a solar calendar whose months track the seasons. Farvardin has 31 days, as do the next five months; the final six months generally have 30 days, with the last month having 29 or 30 depending on the year. This structure differs from the Islamic Lunar Hijri calendar, whose months move through the seasons.
Tir, Khordad, and Ordibehesht are also Persian month names, but none is the first month. Ordibehesht is the second month, Khordad the third, and Tir the fourth. Nowruz therefore marks 1 Farvardin.