13 Month Calendar – International Fixed Calendar, Cotsworth Calendar Explained

Discover an alternative way of measuring time with the 13 Month Calendar, based on the International Fixed Calendar.

The International Fixed Calendar was a proposed reform of the Gregorian calendar, designed by Moses B. Cotsworth and first introduced in 1902. It is also known as the Cotsworth Plan, Cotsworth Calendar, Eastman Plan, or Yearal.

This calendar divides the year into 13 equal months, each consisting of 28 days. Every month contains exactly four weeks, creating a perfectly balanced and predictable system where the same dates always fall on the same weekdays.

How the 13 Month Calendar Works:

• 13 months per year

• 28 days in each month

• 4 weeks per month

• Total of 364 days

• One additional “Year Day” outside the weekly cycle

• Leap years include an extra leap day

The extra month is traditionally called Sol and is placed between June and July.

Materials: birch plywood 3 mm

Colors: rosewood, old oak

Dimensions: M - 30х22,5 сm/ 11.8x8.7"; L - 30х40 сm/ 11.8x15.8"

Personalization on the back side at the bottom right

Why This Calendar Is Unique:

• Perfect monthly symmetry

• Consistent weekly structure

• No shifting weekdays from year to year

• Historically proposed as a global calendar reform

Perfect For:

• Calendar and history enthusiasts

• Educational displays and learning spaces

• Office, study, or library décor

• Unique gifts for thinkers and planners

• Conversation-starting wall art

📌 This calendar is presented for educational and decorative purposes. It is not an official calendar system in modern use.