Gregorian to Shamsi: convert any date the easy way

You have a Gregorian date, a birthday, a deadline, a date on a certificate, and you need it in the Persian calendar. The arithmetic is doable by hand, but it’s fiddly enough near month and year boundaries that most people get it slightly wrong.

Set the Gregorian side to your date and read the Shamsi result:

The quick mental version

If you only need the rough Persian year, the rule is short:

1. Take the Gregorian year.
2. Subtract 621 for most of the year, or 622 if your date is before Nowruz (1 Jan to ~20 March).

So 5 May 2026 is in 1405, while 5 February 2026 is still 1404, because February falls before Nowruz. That single boundary is where the “just subtract 621” shortcut quietly breaks.

Why the day and month need care

Getting the year is the easy part. The day-of-month is harder because the two calendars don’t start their months on the same days, and Persian month lengths differ from Gregorian ones (the first six Persian months have 31 days, for instance). So a date near the end of a month can land in a different month once converted.

There’s also a quiet trap with time zones. If you convert using a tool that works in timestamps rather than plain calendar dates, a date near midnight can shift by a day depending on the zone. This converter uses a date-only model, so the day you put in is the day it converts, with no timezone surprises.

Worked example

Take 20 March 2025. It’s right on the Nowruz boundary, so it’s a good stress test. It converts to 30 Esfand 1403, the last day of the Persian year 1403 (a leap year, which is the only reason 30 Esfand exists that year — the leap rule comes from the calendar’s 33-year cycle, source: Encyclopædia Britannica, “Iranian calendar”). The very next day, 21 March 2025, is 1 Farvardin 1404, the start of the new Persian year. Miss the boundary by one day and you’d be a whole year off. Details on that drift live in why Nowruz isn’t always on the same Gregorian day.

Going the other way

Converting Shamsi back to Gregorian uses the same logic in reverse (add 621, or 622 before Nowruz). If that’s what you need, see today’s date in the Persian calendar for reading the current date, or just flip the converter to enter a Shamsi date. For a birthday specifically, the age calculator will also give your exact age in either calendar.

In short: the year is a quick subtraction, but the day and month are where mistakes hide, so convert the exact date when it matters.