Frequently asked questions
The questions people ask most about calendars — how they work, why they disagree, and how to read them here. General interest, not a claim of authority; where a date is an estimate, the site says so.
The basics
What calendar does the world use today?
Most of the world runs its civil life on the Gregorian calendar, the solar calendar introduced in 1582 and now the international standard for business and government. It is far from the only one in use, though: the Hebrew, Islamic, Persian, Chinese, Hindu and Ethiopian calendars, among many others, remain in daily religious and cultural use — often written alongside the Gregorian date.
How many calendars are there?
There is no fixed number. Dozens are in active civil or religious use around the world, and many more are historical, regional, or reconstructed. All Calendars Now tracks 56 at once, grouped into ten families — from the living calendars of faith and state to the reckonings of invented and fictional worlds.
Why do calendars show different years for the same day?
Because each counts from a different epoch — its own year zero. The Gregorian year counts from the traditional birth of Christ, the Islamic year from the Hijra in 622 CE, the Hebrew year from a calculated date of Creation, and Unix time from the first of January 1970. The day is the same; only the starting line differs.
What is today’s date?
That depends entirely on which calendar you ask — which is the whole point of this site. Right now it is one date on the Gregorian calendar, another on the Hebrew, another again on the Chinese, and All Calendars Now shows them all at once for the very same instant.
How calendars work
What is the difference between a lunar, solar, and lunisolar calendar?
A solar calendar follows the sun and the seasons, like the Gregorian. A lunar calendar follows the phases of the moon and makes no correction to the solar year, so it drifts about eleven days earlier each year — the Islamic calendar is the classic case. A lunisolar calendar follows the moon but inserts a leap month every few years to keep its months in step with the seasons, as the Hebrew, Chinese and Hindu calendars do.
What is a leap year, and why is it needed?
The Earth takes about 365.2422 days to circle the sun — not a whole number. A calendar of exactly 365 days would slip against the seasons by a day every four years, so most solar calendars practise intercalation: adding a leap day, or in lunisolar calendars a whole leap month, to catch up.
Why does the Islamic date fall earlier every year?
Because it is a pure lunar calendar of twelve lunar months with no leap month. Twelve synodic months run about eleven days short of a solar year, so each Islamic year begins roughly eleven days earlier against the Gregorian calendar, cycling through all the seasons over about 33 years.
What is an epoch?
An epoch is the zero point a calendar counts from — the moment it calls the beginning. The Hijra is the epoch of the Islamic calendar, the first of January 1970 is the epoch of Unix time, and the Battle of Yavin is the epoch of the Star Wars calendar.
Reading this site
How does this site work out all these dates?
Everything is computed live in your browser, in your own time zone, for a single shared instant. The living calendars come straight from your browser’s own internationalization engine, so they match your operating system exactly; the historical, indigenous, invented and fictional ones are computed from published formulas.
Are these dates accurate?
The real calendars are exact. A few are approximate by nature and say so on their own page — the French Republican and Baháʼí years turn on the astronomical equinox, and the Maya and Aztec counts rest on the standard correlations. The fictional calendars are anchored to where their own canon places year zero, and those anchors are labelled estimates.
Why do the fictional calendars drift instead of matching our years?
Because a second is a second everywhere. This site never speeds up a clock to force another world’s day to end at our midnight, so a world whose day or year is a different length simply drifts against ours. That is the honest result — and, we think, the more interesting one.
Can I convert a specific date instead of seeing right now?
Yes. The date converter lets you pick any day on the Gregorian calendar and read it at once in every system here — real, invented and fictional.
Particular calendars
What is today’s date in the Mayan calendar?
The Maya kept time in several interlocking counts: the Long Count of days since a mythic creation in 3114 BCE, the 260-day sacred Tzolkʼin, and the 365-day Haabʼ. All Calendars Now shows all of them for the current instant, using the standard GMT correlation.
What year is it in the Hebrew, Chinese, or Islamic calendar?
Each counts from its own epoch, so the numbers differ widely. The Hebrew year sits in the 5780s, counted from Creation; the Islamic year in the 1440s, counted from the Hijra; and the Chinese year is named by the sexagenary cycle of stems and branches rather than simply numbered. All Calendars Now shows each one live.
What is the Star Wars or Discworld date?
The site places the current instant on their in-universe calendars. The Star Wars date is counted in years before or after the Battle of Yavin on the Galactic Standard Calendar; the Discworld date runs on its own eight-day week, with the octeday. Both anchors are, of course, affectionate estimates.
What was the French Republican calendar?
A radical reform of the 1790s that broke the year into twelve thirty-day months of three ten-day décades, opened at the autumn equinox, with five or six festival days at the end. It lasted about twelve years before Napoleon abolished it. All Calendars Now still keeps its time.
The sun and moon
Why is it still light after the sun has set?
Because the upper air goes on scattering sunlight after the sun itself has dropped below the horizon. That lingering light is twilight, and it is graded by how far the sun has fallen: civil twilight to 6° below, nautical twilight to 12°, astronomical twilight to 18°, after which it is properly night.
How long does twilight last?
It depends on where you are and the time of year. Near the equator the sun drops almost straight down and civil twilight can be over in twenty minutes; the further from the equator, the more slanting the descent and the longer the light lingers. Far enough north in summer the sun never falls 6° below the horizon at all, and the twilight simply runs until dawn.
What does this site mean by the length of the day?
Two things, and it shows both. The first is sunrise to sunset — the sun genuinely above the horizon. The second adds civil twilight at either end, which is the light you can actually see by, and at middle latitudes runs about an hour longer.
Why does this site ask for my location?
Only to work out sunrise and sunset where you are, which a time zone alone cannot tell it. Your coordinates are used on your device and never sent anywhere, and everything else on the site — every calendar, every clock — works perfectly well without them.
What is the moon phase shown at the top?
The moon’s current place in its cycle from one new moon to the next, with the percentage of its face lit. That cycle — the synodic month of about 29.5 days — is what every lunar and lunisolar calendar on this site is built on.
What does “waxing gibbous” mean?
Waxing means the lit part is still growing, on its way from new moon to full. Gibbous means more than half the face is lit but it is not yet full — from the Latin for a hump, which is what that lopsided shape looks like. So a waxing gibbous moon is the fat, not-quite-full moon of the few nights before the full one.
Why is a quarter moon half lit?
Because the quarter counts how far the moon has travelled through its cycle, not how much of it you can see. At first quarter it is a quarter of the way from one new moon to the next — and from Earth that works out as exactly half the face lit.
Why do so many calendars start their months at the new moon?
Because a month was originally a moon. The cycle from one new moon to the next is about 29.5 days, plain to see and the same for everybody, which made it the obvious unit long before anyone could measure a year accurately. The Hebrew, Islamic, Chinese and Hindu calendars all still open their months on it — the Islamic traditionally on the first thin crescent sighted after it.
Clocks and standards
What is the difference between GMT, UTC, and atomic time?
GMT is the old mean solar time at Greenwich. UTC is the modern civil standard, kept in step with the turning Earth by the occasional leap second. Atomic time (TAI) is the raw count of the world’s atomic clocks, which takes no leap seconds at all — and so now runs 37 seconds ahead of UTC.
What is a Julian Day Number?
A continuous count of days used by astronomers since the first of January 4713 BCE. It sidesteps every calendar’s months and leap rules, which makes measuring the interval between two dates trivial. Despite the shared name it has nothing to do with the Julian calendar.
What is Unix time?
The number of seconds elapsed since midnight UTC on the first of January 1970 — the way most computers store a moment internally. All Calendars Now shows it ticking up second by second.
What is Swatch Internet Time?
A 1998 scheme that split the day into 1000 “.beats” on a single worldwide clock with no time zones, so that @500 is the same instant everywhere. A curiosity now, but All Calendars Now keeps it running.
Want the vocabulary behind the answers? Browse the glossary of timekeeping, or see this moment in every calendar at once.