Seasonal Drift: 10,000 CE
How far fixed-year systems desynchronize from the tropical year at 10,000 CE.
Calendars side by side
Start from 1 CE, compare with today, and inspect how each calendar labels the same day. Click any matrix cell for details and formulas.
Range: 8000 BCE to 12,000 CE
17 calendar systems
Clickable sync matrix
Drift diagnostics
Birthday Age Converter
Enter your birthday and compare your age today across different calendar year systems.
Synchronization Matrix
Click any cell to inspect derivation details and assumptions.
Seasonal Flip: Hijri New Year
Estimated time for Islamic New Year to traverse all seasons twice.
Fastest Breakers
Approximate long-run stability ranking by mean year-length error.