The notation of the leap day has been changed from xxxx.0.13 to xxxx.0.4. This is because the leap day rule is based on the number 4. In fact, it can be thought of as an extension of the 4x13 pattern of weeks.

Each year consists of 13 weeks of each color summing to 52 weeks (and 1 day). Each 4 year* leap day cycle read more...

Heptagram Weeks

Every 28 day month on the calendar has four heptagrams, one for each calendar color. A heptagram week is the seven day cycle that occurs on a single heptagram over the course of the month. Every day on the heptagram week is three days apart from every other day.

The pattern of Sunday, Monday, read more...

Ideally, the equinoxes and solstices would be appear on the calendar as a month-day alignment exactly on the top, right, bottom, and left positions. This, however, would not be possible for a static calendar as the days of the equinoxes and soltices vary a little bit.

It turns out the top, right, bottom, and left read more...

Digital Roots and the Number Nine

The month-day alignments are those twelve days on the calendar where the day circle is in the center of the month circle. The thirteenth month lies in the center of the calendar and therefore does not have a month-day alignment. These twelve dates are:

1.1

2.3 read more...

Welcome to Calendar 13, a website devoted to a version of the 13 month, 28 day calendar developed by me (Cody Jassman).

It is a free concept for anyone's use or adaption as it is itself a borrowed idea. It is based on the 13 month, 28 day diagram created by John Michell in his book “The Dimensions of Paradise”. read more...