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Perpetual Calendar

Any month or year from 1 to 9999, with ISO week numbers and the years that share its calendar.

January 2026

January 2026
WkSuMoTuWeThFrSa
1123
245678910
311121314151617
418192021222324
525262728293031

2026 starts on a Thursday. Same calendar as: 1970, 1981, 1987, 1998, 2009, 2015, 2037, 2043, 2054, 2065, 2071, 2082.

Why there are only 14 calendars

Every year's layout is decided by just two facts: which weekday 1 January falls on (7 options) and whether February has 29 days (2 options). Seven times two is fourteen, so a drawer of fourteen printed calendars would cover every year there has ever been in the Gregorian system. The hard part is knowing which one to pull out, and that is what the "same calendar as" line above does for you.

A common year is 52 weeks and 1 day long, so the next year starts one weekday later. After a leap year it jumps two. That uneven stepping is why common years repeat in a 6, 11, 11-year rhythm, while leap years repeat every 28 years, until a skipped century leap year (like 2100) breaks the pattern.

Questions people ask

What is a perpetual calendar?
A calendar that works for any year, not just one. Old printed versions used a table of year letters and month grids; this one calculates each month directly, from year 1 to 9999.
Why do some years share the same calendar?
A calendar is fixed by two things: the weekday of 1 January and whether the year is a leap year. That gives only 14 possible layouts, so years repeat. Common years usually repeat after 6 or 11 years (sometimes 12 across a skipped century leap year); leap years after 28.
Does it use the Gregorian calendar before 1582?
Yes. Dates before the Gregorian reform (October 1582, later in Britain and its colonies in 1752) are shown in the proleptic Gregorian calendar, which is what ISO 8601 uses. Historical documents from before the switch may be in the Julian calendar; use the date converter to translate.
Can I reuse an old calendar?
Yes, if it is one of the "same calendar" years listed next to the grid. A 2015 wall calendar, for example, has the same weekdays as 2026.