Century years
Skip every 100 years, add back every 400.
A little too much
Adding a day every four years adds a little too much over a long time.
How can the calendar be corrected?
What this lesson covers
The idea
Since a leap day every four years adds slightly too much, leap years are skipped every 100 years, but every 400 years the leap year is added back, keeping the calendar matched with the seasons.
A little too much
Adding a day every four years adds a little too much over a long time.
How can the calendar be corrected?
- Skip a leap year every 100 years
- Never add a leap day
- Add two leap days every year
Check century years
Look at 1700, 1900, 1600 and 2000.
Keeping close to the seasons
A leap day every four years adds slightly too much, so leap years are skipped every 100 years, like 1700, 1800 and 1900. But skipping all of them would make the calendar lag behind, so every 400 years a leap year is added back, like 1600 and 2000.
Leap years are skipped every 100 years (1700, 1800, 1900) but added back every 400 years (1600, 2000).
Notes
Skip leap years every 100 years, add back every 400.
Check yourself
Which of these years is not a leap year?
Which of these century years is a leap year?
A leap day every four years adds slightly too much, so leap years are …
Why is a leap year added back every 400 years?
- 1600. 1600 is added back as a leap year.
- 1900 — correct. Yes!
- 2000. 2000 is added back as a leap year.
- 1700. 1700 is skipped.
- 1800. 1800 is skipped.
- 2000 — correct. Yes!
- skipped every 100 years — correct. Yes!
- added twice. They are skipped every 100 years.
- never skipped. Some are skipped to correct the extra.
- To make the year longer. It is added back so that the calendar does not lag.
- Skipping all would make the calendar lag behind the seasons — correct. Yes!
- Because 400 is a lucky number. It keeps the calendar matched with the seasons.