International Fixed Calendar
Updated: 12/11/2025, 4:52:29 PM Wikipedia source
The International Fixed Calendar (also known as the Cotsworth plan, the Cotsworth calendar, the Eastman plan or the Yearal) was a proposed reform of the Gregorian calendar designed by Moses B. Cotsworth, first presented in 1902. The International Fixed Calendar divides the year into 13 months of 28 days each. A type of perennial calendar, every date is fixed to the same weekday every year. Though it was never officially adopted at the country level, the entrepreneur George Eastman instituted its use at the Eastman Kodak Company in 1928, where it was used until 1989. While it is sometimes described as the 13-month calendar or the equal-month calendar, various alternative calendar designs share these features.
Tables
Common arrangement of all months · Rules
Sun
Sun
Days of the week
Sun
Days of the week
Mon
Days of the week
Tue
Days of the week
Wed
Days of the week
Thu
Days of the week
Fri
Days of the week
Sat
Days of the week
Hol
01
01
Days of the week
01
Days of the week
02
Days of the week
03
Days of the week
04
Days of the week
05
Days of the week
06
Days of the week
07
Days of the week
Leap Day, Year Day
08
08
Days of the week
08
Days of the week
09
Days of the week
10
Days of the week
11
Days of the week
12
Days of the week
13
Days of the week
14
15
15
Days of the week
15
Days of the week
16
Days of the week
17
Days of the week
18
Days of the week
19
Days of the week
20
Days of the week
21
22
22
Days of the week
22
Days of the week
23
Days of the week
24
Days of the week
25
Days of the week
26
Days of the week
27
Days of the week
28
Days of the week
X*
| Days of the week | |||||||
| Sun | Mon | Tue | Wed | Thu | Fri | Sat | Hol |
| 01 | 02 | 03 | 04 | 05 | 06 | 07 | Leap Day, Year Day |
| 08 | 09 | 10 | 11 | 12 | 13 | 14 | |
| 15 | 16 | 17 | 18 | 19 | 20 | 21 | |
| 22 | 23 | 24 | 25 | 26 | 27 | 28 | X* |
· Rules
Starts on fixed day 1
Starts on fixed day 1
IFC
Starts on fixed day 1
Matching dates on the Gregorian calendar
Ends on fixed day 28
January
January
IFC
January
Matching dates on the Gregorian calendar
January 1
Matching dates on the Gregorian calendar
January 28
February
February
IFC
February
Matching dates on the Gregorian calendar
January 29
Matching dates on the Gregorian calendar
February 25
March
March
IFC
March
Matching dates on the Gregorian calendar
February 26
Matching dates on the Gregorian calendar
March 25*
April
April
IFC
April
Matching dates on the Gregorian calendar
March 26*
Matching dates on the Gregorian calendar
April 22*
May
May
IFC
May
Matching dates on the Gregorian calendar
April 23*
Matching dates on the Gregorian calendar
May 20*
June
June
IFC
June
Matching dates on the Gregorian calendar
May 21*
Matching dates on the Gregorian calendar
June 17*
Leap Day*
Leap Day*
IFC
Leap Day*
Matching dates on the Gregorian calendar
June 17
Sol
Sol
IFC
Sol
Matching dates on the Gregorian calendar
June 18
Matching dates on the Gregorian calendar
July 15
July
July
IFC
July
Matching dates on the Gregorian calendar
July 16
Matching dates on the Gregorian calendar
August 12
August
August
IFC
August
Matching dates on the Gregorian calendar
August 13
Matching dates on the Gregorian calendar
September 9
September
September
IFC
September
Matching dates on the Gregorian calendar
September 10
Matching dates on the Gregorian calendar
October 7
October
October
IFC
October
Matching dates on the Gregorian calendar
October 8
Matching dates on the Gregorian calendar
November 4
November
November
IFC
November
Matching dates on the Gregorian calendar
November 5
Matching dates on the Gregorian calendar
December 2
December
December
IFC
December
Matching dates on the Gregorian calendar
December 3
Matching dates on the Gregorian calendar
December 30
Year Day
Year Day
IFC
Year Day
Matching dates on the Gregorian calendar
December 31
| IFC | Matching dates on the Gregorian calendar | |
| Starts on fixed day 1 | Ends on fixed day 28 | |
| January | January 1 | January 28 |
| February | January 29 | February 25 |
| March | February 26 | March 25* |
| April | March 26* | April 22* |
| May | April 23* | May 20* |
| June | May 21* | June 17* |
| Leap Day* | June 17 | |
| Sol | June 18 | July 15 |
| July | July 16 | August 12 |
| August | August 13 | September 9 |
| September | September 10 | October 7 |
| October | October 8 | November 4 |
| November | November 5 | December 2 |
| December | December 3 | December 30 |
| Year Day | December 31 | |
References
- See the table in Cotsworth 1905, p. i
- Cook, Anna J, (2024) A Man Beyond Time: Moses Cotsworth's fight for the 13-month calendar Independent Publishing Network
- Cotsworth 1905.
- "Eastman Kodak going on our calendar"https://www.newspapers.com/article/florence-morning-news-eastman-kodak-goin/151919315/
- Cotsworth suggested "Mid" as an alternative name. See his address in Royal Society of Canada, Proceedings and Transactio
- Hirossa Ap-Iccim, "An Essay on the British Computation of Time, Coins, Weights, and Measures" The Gentleman's Magazine,http://www.bodley.ox.ac.uk/cgi-bin/ilej/image1.pl?item=page&seq=1&size=1&id=gm.1745.7.x.15.x.x.377
- Cotsworth 1905, p. i.
- Duncan Steel, Marking Time: The Epic Quest to Invent the Perfect Calendar (New York: John Wiley & Sons, 2000), page 309
- Moses Bruines Cotsworth, Calendar Reform (London: The International Fixed Calendar League, 1927), Preface.
- Jewish Telegraphic Agencyhttps://www.jta.org/2012/02/24/the-archive-blog/calendar-reform-and-joseph-herman-hertz
- Congressional Recordhttps://books.google.com/books?id=-yhW_jXDsUgC&pg=PA2698
- Journal of Calendar Reform volume 16, number 4 (1944): 165-66