The world very nearly adopted a calendar with 13 months of 28 days
A detailed history of the League of Nations proposal and the religious campaign known as the Battle for the Sabbath.
News and the wider web
What others publish about 13-month calendars
A curated map of reporting, historical coverage, reference pages and independent projects. Links go to the original publisher; Google is used only to discover new items.
The Death and Life of the 13-Month Calendar
A compact account of Cotsworth, George Eastman, business support and the decline of international calendar reform.
The case for an entirely new calendar
A broader look at permanent-calendar proposals and why changing a global convention is difficult.
Kodak Used a Calendar That Had 13 Months
A short, accessible introduction centered on Kodak’s internal use of the International Fixed Calendar.
Business & Finance: New Calendar Progress
Contemporary reporting from the height of Eastman’s campaign, useful as a historical primary source for the movement’s claims and support.
The International Fixed Calendar: A Better Calendar That Almost Happened
A recent long-form explainer covering the fixed layout, Kodak and the barriers to adoption; historical details should still be checked against primary sources.
A ONU Abraça uma Nova Era com um Calendário de 13 Meses: O Futuro da Gestão do Tempo Começa com a Cal.com
An April Fools’ marketing article that imagines the United Nations adopting a 13-month calendar. Its central claim is fictional, not a UN announcement.
Would a calender with 13 months, all of them having 28 days, work? Also every year there is one day that isn't part of any month and is solely there to help with the lunar cycle.
A community discussion about 13 equal months and days outside the week, with comments on the International Fixed Calendar, lunar alignment, seasons and worldbuilding.
13 meses de 28 dias: Conheça o inusitado Calendário Fixo Internacional
A Portuguese-language historical overview of Cotsworth’s proposal, Kodak and twentieth-century opposition. Its contextual claims should still be checked against primary sources.
The 13-Month Calendar Concept
A user-uploaded English document about 13-month proposals, Kodak and adoption barriers. Authorship, provenance and automated enhancements require independent verification.
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List reviewed on Aug 31, 2026