What day is it — everywhere, and everywhen?
The same instant, read through more than two dozen calendars built by civilizations across five thousand years. Pick any Gregorian date below to see it refracted through them all.
Global Calendar Conversion Table
Every supported calendar system, evaluated for the date shown in the converter below. Filter by family to compare related systems.
| Calendar | Category | Representation | Year | Month | Day | Notes |
|---|
Interactive Date Converter
Convert from any supported calendar system. Pick a source calendar and enter a date — every section on this page updates from this one control.
World Calendar Timeline
Origins, reforms, and transitions — the moments civilizations changed how they counted days.
Calendar Encyclopedia
History, geography, religious context, astronomical basis, epoch, leap-year logic, and conversion method for every system on this page.
Astronomical Foundations
Every calendar is an attempt to reconcile three cycles that don't divide evenly into each other: the day, the lunar month, and the solar year.
The Solar Year & the Seasons
Earth's elliptical orbit and 23.4° axial tilt produce the equinoxes and solstices that anchor most solar calendars. Drag to move Earth around its orbit.
The Lunar Month
The synodic month (new moon to new moon) averages 29.53 days — never a whole number, which is why every lunar and lunisolar calendar needs a correction scheme.
Key quantities
Calendar Comparison Engine
Solar, lunar, and lunisolar calendars trade off simplicity against how well they track the seasons. "Drift" is how far a fixed calendar date wanders from its original astronomical anchor per century if left uncorrected.
| Calendar | Type | Average year length | Leap correction | Drift vs. tropical year |
|---|
Era & Epoch Explorer
The same Gregorian date, read through the major year-counting systems layered on top of (or independent from) the calendars above.
Mathematical Conversion Lab
Every conversion on this page reduces to one pivot: the Julian Day Number (JDN), a single running count of days used by astronomers since 1583. Here's the arithmetic, worked for the date above.