Featured story
Start with the calendar question that explains why some years have an extra day.
A tiny calendar correction with a very big job
Earth’s seasonal year is not exactly 365 days long. Explore how leap days keep civil dates aligned with the seasons and why century years follow a special rule.
Read the guide →Editor’s picks
Explore some of our most useful guides to birthdays, calendars and time.
Why Do Leap Years Exist?
The precise calendar correction that keeps dates aligned with the seasons.
🗓️Why Does February Have 28 Days?
Roman calendar history explains why the shortest month stayed short.
🌍The Gregorian Calendar Explained
How a sixteenth-century reform became the dominant civil calendar.
🕯️Why Do We Blow Out Birthday Candles?
Explore what historians can—and cannot—say about the familiar wish ritual.
Explore by category
Follow the topics that make you curious.
Birthdays
Cakes, candles, celebrations and the stories behind birthday traditions.
📅Time & Calendars
Leap years, February, weeks and the systems that organise everyday dates.
✨Traditions & Symbols
Birthstones, flowers and the cultural meanings attached to months and birthdays.
🕰️Birth years
Explore the world people were born into through Time Capsules and year profiles.
Featured collections
Follow a connected learning path instead of a single article.
A common Gregorian year contains 52 full weeks plus one day. That extra day is why the weekday for a given date usually shifts forward from one year to the next.
More guides to explore
Discover birthstones, birth flowers, age calculation and a curated symbols collection.