How the Persian (Solar Hijri) calendar works

The Persian calendar is elegant once you see its parts: a solar year, a clean month structure, a precise leap rule, and an era count. Here’s the whole thing in one place.

Want to see it in action? Convert any date between the two calendars:

1. It’s solar, and tied to the equinox

The calendar tracks the Earth’s orbit around the Sun, and its year begins at the vernal equinox, not on a fixed page-date. That anchor keeps it locked to the seasons, Nowruz always lands at the start of spring. This is what makes it a Solar Hijri calendar, distinct from the lunar Islamic calendar. More on that distinction in is the Persian calendar lunar or solar, and on the equinox choice in why the Persian year starts at the spring equinox.

2. Twelve months, in a clean pattern

The year divides into 12 months with a regular structure:

That’s 365 days in a common year, 366 in a leap year. The first month is Farvardin, and the full list with Gregorian overlaps is in the Persian calendar months.

3. The 33-year leap cycle

A solar year is about 365.2422 days, so the calendar must absorb the leftover ~0.2422 day. It does this by adding a leap day, always 30 Esfand, at the end of the year. Persian leap years aren’t “every four years,” they’re distributed as 8 leap years across a 33-year cycle, with an occasional five-year gap, which keeps the equinox precisely in place. The mechanics are in Persian (Jalali) leap years, explained, and the leap day itself in 30 Esfand explained.

4. The era count (why it’s in the 1400s)

The calendar counts years from the same era as the Islamic calendar, the Hijra in 622 CE, but measures them as solar years. That’s why the current Persian year is in the 1400s while the Gregorian year is in the 2000s, an offset of roughly 621–622 years. The full explanation is in what year is it in the Persian calendar.

5. Mapping to Gregorian

Putting it together, converting between the two means handling the year offset, the differing month lengths, and the differing leap rules, all at once, with extra care around the Nowruz boundary in March. The complete how-to is in Shamsi and Gregorian conversion, explained, and for the reverse direction, Gregorian to Shamsi.

Why it’s considered accurate

Because it pins the year to the actual astronomical equinox and arranges leap days to keep it there, the Persian calendar stays very close to the true solar year over long spans, more accurately than a purely arithmetic four-year rule. That precision is a direct result of the equinox anchor plus the 33-year cycle working together. For example, the tropical year is about 365.2422 days (source: Encyclopædia Britannica, “tropical year”), and the 33-year cycle’s 8 leap days (8 ÷ 33 = 0.2424) track that fraction almost exactly, which is why the new year holds to the equinox far better than the Gregorian 0.2425 approximation over the same span.

That’s the whole machine: solar year, twelve clean months, a 33-year leap cycle, and an era from 622 CE. To see any date move between the two systems, use the converter.