Persian vs Gregorian calendar

At a glance

One year, two calendars

The ribbon below lays a Gregorian year over the Persian months, day by day. Move along it to read any date in both calendars, or switch years to see Nowruz move between 20 and 21 March.

One year, two calendars

2026

Gregorian Shamsi

Saturday, March 21, 2026 = Saturday, 1 Farvardin 1405

Three things stand out. Persian months begin around the 20th–23rd of a Gregorian month, so a Persian month always spans two Gregorian ones. The Persian year changes in March, not January. And the long Persian months of the first half-year, 31 days each, line up with the long northern summer.

Why the year differs by 621 or 622

Both calendars count years continuously, but they start each year at a different point. Between Nowruz and 31 December, the Persian year is the Gregorian year minus 621. Between 1 January and the day before Nowruz, it is minus 622.

Gregorian − 622 1 Jan → day before Nowruz

Nowruz

Gregorian − 621 Nowruz → 31 Dec

This is the single most common source of conversion mistakes. If you only know a Persian year — say a birth year of 1360 — the matching Gregorian year is 1981 if the birthday falls between Farvardin and Dey 10 or so, and 1982 if it falls in late Dey, Bahman or Esfand. To be sure, convert the full date.

Try 15 Bahman 1360

Different New Year’s Days

The Gregorian year begins on 1 January, a date with no astronomical meaning. The Persian year begins on Nowruz, the first day of spring: the day of the March equinox if it occurs before noon Iran time, otherwise the next day. Because the equinox drifts a few hours later each year and is pulled back by Gregorian leap days, Nowruz falls on 20 or 21 March in the Gregorian calendar. Read more in Nowruz and the Persian New Year.

Leap years: a rule versus the sky

The Gregorian calendar decides leap years arithmetically: every year divisible by 4, except century years not divisible by 400. You can check any year with pencil and paper.

The Persian calendar decides them astronomically: a year is a leap year when 366 days separate one Nowruz from the next. In practice this produces a leap year every four years, with a five-year gap roughly every 33 years — 1403 was a leap year, and the next is 1408.

The leap days also sit in different places. The Gregorian leap day, 29 February, falls in the Persian month of Esfand; the Persian leap day, 30 Esfand, falls on 19, 20 or 21 March. That is why a Persian date can map to a different Gregorian day from one year to the next, even for the same month and day.

Months that don’t line up

Gregorian

1. 31 Jan
2. 28+ Feb
3. 31 Mar
4. 30 Apr
5. 31 May
6. 30 Jun
7. 31 Jul
8. 31 Aug
9. 30 Sep
10. 31 Oct
11. 30 Nov
12. 31 Dec

Shamsi

1. 31 Farvardin
2. 31 Ordibehesht
3. 31 Khordad
4. 31 Tir
5. 31 Mordad
6. 31 Shahrivar
7. 30 Mehr
8. 30 Aban
9. 30 Azar
10. 30 Dey
11. 30 Bahman
12. 29+ Esfand

The Persian calendar puts its long months first and its short ones last; the Gregorian calendar alternates more or less at random. Neither month boundary lines up with the other, which is why mental arithmetic like “Farvardin is April” is only roughly true: 1 Farvardin is 20 or 21 March, and 1 Ordibehesht is 20 or 21 April.

Which calendar is more accurate?

Both are excellent at tracking the seasons. The Gregorian calendar’s average year is about 26 seconds longer than the solar year, a drift of roughly one day in three thousand years or so. The Persian calendar has no long-term drift at all, because each year is re-anchored to the observed equinox — but that strength is also its practical weakness: you need astronomical calculation, or a published calendar, to know future leap years with certainty. The Gregorian calendar trades a tiny drift for a rule anyone can compute.

Converting between them

Because month lengths, leap days and New Year’s Days differ, the only reliable conversion is day by day — exactly what the converter does. The date conversion guide covers birthdays, official documents and the most common mistakes.

Sources

1. Kazimierz M. Borkowski, “The Persian calendar for 3000 years”, Earth, Moon and Planets 74 (1996): 223–230. doi:10.1007/BF00055188
2. Encyclopaedia Britannica, “The Gregorian calendar”. britannica.com
3. M. Heydari-Malayeri, “A concise review of the Iranian calendar” (2004). arXiv:astro-ph/0409620