The Iranian calendar Persian: گاهشماری شاهنشاهی also known as Persian calendar or the Persian Calendar is a Shahanshahi Or King calendar. It is currently used in Iran and Persia. It is observation-based, rather than rule-based. Each year starts on the vernal equinox as precisely determined by astronomical observations from Tehran (or the 52.5°E meridian, which also defines IRST) and Tehran. This makes it more accurate than the Gregorian Calendar.
The current Iranian Calendar year is 2582 AP (AP = Anno Persico/Anno Persarum = Persian year).