Explore any calendar year

Check whether a year is a leap year, how many days it contains, its first weekday, ISO week count and next matching calendar.

Year calendar facts

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Year length and the weekday of January 1 determine the layout of an entire calendar. Start with the features used to compare two calendar years.

Most years divisible by four contain February 29, but century years have an additional test. See the Gregorian leap-year rule with examples.

A future year can place every date on the same weekday. Learn how to find years with the same calendar.

Compare length, weekday alignment, weeks and dates across any two calendar years.

Use the Gregorian rule to identify past and future leap years.

Find years whose dates fall on the same weekdays.

Understand how named spans of years are numbered.

Calculate complete elapsed years without off-by-one birthday errors.

Calculate age from a birth date or estimate it from a birth year.