How Gregorian Leap Years Actually Work: The 400-Year Cycle Explained
Why are some century years like 2000 leap years while 1900 and 2100 are not? Explore the astronomical math and history behind the Gregorian calendar leap rule.
Category: Date & Calendar Math
In-depth explorations of calendar standards, leap cycles, daylight saving transitions, and date algorithms.
ISO-8601 Explained: Why Week 1 of a Year Can Begin in December
Demystifying the international ISO-8601 standard. Discover why the ISO week-year can differ from the calendar year and how weeks are numbered globally.