Is the Persian calendar lunar or solar?

This one causes a surprising amount of confusion, partly because two different “Hijri” calendars share that name. People assume anything connected to the Islamic era must be lunar. The Persian calendar isn’t.

Solar vs lunar, in one practical difference

A solar year is about 365.24 days, the time the Earth takes to orbit the Sun (source: Encyclopædia Britannica, “tropical year”). A lunar year of 12 lunar months is about 354 days, roughly 11 days shorter. For example, if a lunar date and a solar date line up this year, next year the lunar one will land about 11 days earlier against the seasons. That 11-day gap is the whole reason the two calendars behave so differently:

• The Persian (Solar Hijri) calendar stays locked to the seasons. Nowruz is always at the start of spring, every year, because the calendar is built around the equinox.
• The Islamic (lunar Hijri) calendar drifts against the seasons by about 11 days a year, which is why dates like Ramadan move earlier through the Gregorian year over time.

So both can be called “Hijri” (both count eras from 622 CE), but only the Persian one is solar and season-locked. Side by side:

Why “1404” is not the same as the Islamic Hijri year

Because one is solar and one is lunar, their year numbers have drifted apart even though they started together. The Solar Hijri year (currently 1404) and the lunar Hijri year are now several decades apart, and the gap keeps widening by roughly 11 days a year. They are genuinely different calendars that happen to share a starting era, not two names for the same thing.

This matters when you convert dates: a Persian date and an Islamic-calendar date are not interchangeable, and a tool built for one will give wrong answers for the other. The converter here handles the Persian (Shamsi) ⇄ Gregorian mapping specifically.

Is it accurate?

The solar design makes the Persian calendar one of the more accurate in common use. Because it pins the new year to the actual astronomical equinox rather than a purely arithmetic rule, it stays very close to the true solar year over long spans, with the leap-day pattern absorbing the fractional ~0.2422 day each year. The widely used arithmetic version distributes 8 leap years across a 33-year cycle, which is what keeps it in step. The mechanics of that are covered in Persian (Jalali) leap years, explained.

How many months and days

The solar year is divided into 12 months: the first six have 31 days, the next five have 30, and the last month, Esfand, has 29 days (30 in a leap year). That gives 365 days in a common year and 366 in a leap year, the same totals as the Gregorian calendar, just arranged differently. The full month list is in the Persian calendar months, and you can compare the two systems side by side in Gregorian vs Solar Hijri.

The takeaway: Persian = solar and season-locked; Islamic religious calendar = lunar and drifting. If you need to move a Shamsi date to or from Gregorian, the converter does it directly.