Shamsi and Gregorian conversion, explained

If you regularly move dates between the Persian and Gregorian calendars, it helps to understand the whole picture once, rather than memorising shortcuts that break at the edges. This is the overview that ties the details together.

The fastest path is always to convert the exact date:

The three things that differ

1. The year offset. The Solar Hijri year is roughly 621 years behind the Gregorian year, 622 in the window between 1 January and Nowruz (source: Encyclopædia Britannica, “Iranian calendar”). For example, 2026 is mostly 1405, but early-2026 dates before Nowruz are still 1404.

2. The month lengths. The Persian year’s first six months (Farvardin to Shahrivar) have 31 days, the next five (Mehr to Bahman) have 30, and the last, Esfand, has 29 (or 30 in a leap year). The Gregorian calendar has its own irregular pattern, including February’s 28/29. Because the months don’t line up, a date near a month edge can land in a different month after conversion. The full list is in the Persian calendar months.

3. The leap years. Both calendars add a leap day, but by different rules. Gregorian uses “divisible by 4, except centuries not divisible by 400.” The Persian calendar distributes 8 leap years across a 33-year cycle, tied to keeping the equinox in place. They don’t fall on the same years, so a leap-day date in one calendar may be an ordinary date in the other. See Persian (Jalali) leap years, explained and why February has 28 days.

The boundary that trips everyone

The single most common error is treating the year offset as a fixed number. It isn’t, because the Persian year turns over at the equinox in March, not on 1 January. A date in February 2026 is 1404; a date in April 2026 is 1405. Convert across that boundary carelessly and you’re a year off. The reason the equinox date itself wobbles between 20 and 21 March is covered in why Nowruz isn’t always on the same Gregorian day.

A second, quieter pitfall: time zones

If a conversion tool works in timestamps rather than plain calendar dates, a date near midnight can shift by a day depending on the time zone. A date-only approach avoids this entirely, the day you enter is the day that converts. That’s how the converter here is built, which is why a date near midnight never drifts.

Both directions, any date

Everything above works the same in reverse:

• Gregorian → Shamsi: see Gregorian to Shamsi for the step-by-step.
• Shamsi → Gregorian: flip the converter, or read today’s date in the Persian calendar.
• Counting between two dates: the difference tool and days between dates.
• A birthday or age: the age calculator.

Once you see the three moving parts, year offset, month lengths, leap rules, conversion stops being mysterious. For exact results, let the converter handle all three at once.