201 years — leap years, weekdays, week counts and zodiac signs
Every year from 1900 to 2100: whether it is a leap year, how many days it holds, what weekday New Year’s Day falls on, how many ISO weeks it has, and which sign of the sixty-year cycle it carries.
The rule for leap years
Divisible by 4 makes a leap year, divisible by 100 takes it back, divisible by 400 grants it again. That is why 1900 was not a leap year and 2000 was.
Divisible by four, yet not a leap year
Only 1900 and 2100 fall this way here: divisible by 100, not by 400, so the rule takes the day back.
Years of 52 weeks and of 53
ISO counts a week as belonging to the year that holds its Thursday. A year runs to 53 weeks only when it contains 53 Thursdays — that is, when 1 January is a Thursday, or a Wednesday in a leap year.
The sixty-year cycle
Ten heavenly stems and twelve earthly branches advance together, one step each year, so the same pair returns only after sixty years. The animal alone repeats every twelve.
Decade by decade
1880s
1890s
1900s
1910s
1920s
1930s
1940s
1950s
1960s
1970s
1980s
1990s
2000s
2010s
2020s
2030s
2040s
2050s
2060s
2070s
2080s
2090s
2100s
2110s
2120s
How to read this
- Divisible by 4 is a leap year, by 100 is not, by 400 is again.
- A leap year holds 366 days, and February runs to the 29th.
- The ISO week count follows the Thursdays: 53 of them make a 53-week year.
- The sexagenary sign returns every 60 years, the animal every 12.
Frequently asked questions
QWhy is 2100 not a leap year?
Because it divides by 100 but not by 400. The Earth takes 365.2422 days to orbit the Sun, so adding a day every four years overshoots slightly; skipping one every century and restoring it every four centuries settles the difference.
QCan a year really have 53 weeks?
Yes. ISO assigns a week to the year holding its Thursday, and some years contain 53 Thursdays — thirty-six of the 201 years here.
QWhen do people born on 29 February celebrate?
It varies by country. Some treat 28 February as the legal date in common years, others 1 March. A few countries write it into law; most leave it to custom.
QDoes the zodiac animal change on 1 January?
No. It turns at the lunar new year or at the start of spring, so anyone born in January or early February may still carry the previous year’s animal. The signs on these pages count whole calendar years.
QWhy start at 1900?
Because 1900 and 2100 both divide by 4 without being leap years — putting the two exceptions at either end of the range.