Fourteen Different Calendars

Introduction

If you didn’t already know it the 1st January next year will always be on a different day to the 1st January this year. This comes about because:

• for ordinary years with 365 days there are 52 weeks and 1 day remaining,
• for leap years with 366 days there are 52 weeks and 2 days remaining.

This means that:

• if the 1st January is on a Monday in an ordinary year then so is the 31st December. So the next year must have the 1st January on a Tuesday,
• if the 1st January is on a Monday in a leap year then the 31st December is on a Tuesday. So the next year must have the 1st January on a Wednesday.

If there had been 364 days in every year the 1st January would always be on the same day of the week.

As a consequence of all this movement around the week, by the 1st January, next years calendar is always different to this years. That leads to the question: “There’s only seven days in a week so how many different ones do we need? Just seven.” Well the answer is, “No, you need another seven as well, for all the leap years. They too can start on any day of the week.”

Fourteen Different Calendars Are Required

Yes, there are fourteen different calendars required to make all calendars for all years:

• seven are required to allow for the first day of the year occurring on every day of the week for 365 day years;
• another seven are required to cover the same situation for 366 day Leap Years.

I have produced a reference table showing which years in the range 2001 to 2140 start on each day of the week. You can see it here: Fourteen Calendar Table in the Reference Library.

Referrers

1. Print A Long Thin Calendar For Any Year – HC Blog Post

References

1. Fourteen Calendar Table – HC Reference Library
2. Leap Years