What day of the week was I born?

“Were you a Monday’s child?” It’s a fun thing to know, and it’s also a small, well-defined date problem. The weekday of any past date is fixed and computable, no memory required.

The weekday is the same in both calendars

This trips people up, so it’s worth stating plainly: the days of the week run continuously and don’t reset between calendars. 20 March 2025 and its Persian equivalent 30 Esfand 1403 are the same physical day, a Thursday. Converting a date between Shamsi and Gregorian never changes its weekday, because it’s still the same point in time, just labelled differently.

So whether you know your birth date in Gregorian or in Shamsi, the weekday comes out the same.

What that day is called in Persian

Six of the seven names are built by counting from Shanbeh (Saturday), which is where the Persian week begins:

Note the offset: Yekshanbeh means “one after Shanbeh”, so it is the second day of the week, not the first. Only Jom’eh steps outside the counting pattern — Panjshanbeh is perfectly regular, despite a common claim that Thursday breaks it too.

Under Iran’s Labour Code of 20 November 1990, Friday is the paid weekly rest day: section 62 provides that “Friday shall be the workers’ day of weekly rest with pay.” A note to the same section allows another day to be substituted, so a specific workplace may differ.

Every conversion on this site already prints the weekday first, so you see the Persian name on every result without asking for it.

How weekdays repeat

Weekdays run on a tight seven-day loop, so every date in history sits on a fixed day. The pattern shifts in a way that’s easy to picture once you see it.

A common year is 365 days. Divide by 7 and you get 52 weeks plus 1 leftover day. That single leftover is why your birthday lands one weekday later each year: a Tuesday birthday becomes a Wednesday the next year. Then a leap year adds a day, so the shift jumps by two whenever a leap day falls between two of your birthdays.

So the sequence isn’t random. It creeps forward by one most years, two across a leap day, and cycles back around every 28 years in the Gregorian calendar, ignoring the century quirks. The formal by-hand method is the Doomsday rule (source: Doomsday rule on Wikipedia), which involves the usual leap-year adjustments — which is why a tool beats mental arithmetic.

There’s a subtlety with very old dates: countries adopted the Gregorian calendar at different times, so historical weekday answers can depend on which calendar was in local use. For ordinary modern birth dates this isn’t a concern.

A quick sanity check

Some well-known dates make good reference points:

If the tool agrees with these, it’s working — and it does, because it uses the same date engine as the rest of the site.

A quiet pitfall: time zones

As with all date math, the gotcha is timestamps. If a tool uses a date-with-time instead of a plain calendar date, a value near midnight can roll to the previous or next day, and therefore the wrong weekday. A date-only approach avoids this: the day you enter is the day evaluated, so two people checking the same birth date anywhere in the world get the same answer. The same principle is covered in days between dates.

Related date questions

If you want your full age rather than just the weekday, see how old am I in the Persian calendar and the age calculator. To find the gap between two dates, the difference tool helps. And to convert the date itself between calendars, use the converter.