How ChinRooz works
What it does, how it works out a date, and what it deliberately leaves out.
What ChinRooz is
ChinRooz converts dates between the Persian and Gregorian calendars. It is built for people who live with both: filling in an official form, reading a birth certificate, sending an invitation, or working out which day a birthday falls on this year.
It is free, needs no account, and does its work in your browser. There is nothing to install.
How a date is worked out
The Persian calendar is a solar calendar, like the Gregorian one. Its year begins at the spring equinox, so a Persian year stays in step with the seasons instead of drifting through them. That is why converting between the two is a matter of counting days rather than looking up a table: both calendars count real days.
ChinRooz does that counting the same way every time. The same date always gives the same answer, on any device, with no rounding and no guessing. Nothing is sent anywhere to be worked out.
Gregorian dates from 1800 to 2100, and Persian dates from 1178 to 1479.
The window stops there on purpose. Beyond it, the rule that decides which Persian years are leap years is no longer settled, and a converter that answered anyway would be guessing. Rather than hand you a number nobody can check, ChinRooz says the date is outside its range.
Where the Chinese zodiac dates come from
The Chinese year does not start in January. It starts at the lunar new year, which moves. Those dates cannot be worked out from the calendar alone, so ChinRooz does not try: it uses a published table of 200 boundaries, one for every year from 1901 to 2100.
The table is part of the program and is checked when it loads. No service is called while you use the site, so the zodiac works without a connection like everything else.
Source
- Hong Kong Observatory, Gregorian–Lunar Calendar Conversion Table (DATA.GOV.HK)
- Hong Kong Observatory, 1984 Jia-Zi sexagenary-cycle anchor
The Persian sign, and why tables disagree
The Western zodiac signs are the twelve Persian months: Farvardin is Aries, and so on around the year. Because the Persian month begins at the equinox, the sign changes when the month changes — not on a fixed calendar date. Printed tables usually pick a fixed day instead, so near a boundary they can be a day out from what ChinRooz shows. ChinRooz follows the calendar.
Privacy
The dates you type never leave your device. They are not stored, not sent anywhere, and never put in the address bar, so nothing about them can be shared by accident. Page views and loading speed are counted in aggregate and without cookies, by a small script from the site’s hosting provider — enough to know which pages are worth keeping and whether the site is fast enough. That is all it measures.
Working without a connection
After one visit, the converter and the birthday profile keep working with no connection at all. The pages you need are kept by your browser on that first visit, so a tunnel or a dead signal does not stop you converting a date. Longer reading pages, like the zodiac articles, are fetched when you open them.
What ChinRooz does not do
These are missing on purpose:
- No accounts, no sign-in, no saved history.
- No horoscopes, forecasts, or predictions of any kind.
- No personality or compatibility readings — the zodiac pages describe a tradition, not a person.
- No advertising, no visitor profiles, and no tracking across sites or over time.