Fixed Calendar
Artistic representation of Earth in thirteen positions around the Sun
An open initiative

13 months.
A year in balance.

A community exploring a simpler, more regular way to organize time: 13 months, 28 days each, and calendars that remain comparable forever.

Convert a date →Discover the calendar
One year · Thirteen positions · One world
13months per year
28days per month
4exact weeks
1 + 1intercalary days
The idea

A predictable calendar, year after year.

The International Fixed Calendar keeps the Gregorian year's 365 or 366 days, but distributes them regularly. Every date always falls on the same weekday.

01 / 03

Thirteen equal months

Each month has exactly 28 days: four complete weeks that always begin on Sunday.

02 / 03

A month called Sol

Sol sits between June and July, completing thirteen months without changing the seasons.

03 / 03

Days outside the week

Year Day and, in leap years, Leap Day belong to no week.

Try it

Your date, in another rhythm.

Convert both ways. Everything happens in your browser: fast, private, and without sign-ups.

Gregorian date
→
International Fixed Calendar
4 July
2026
Wednesday · month 8/13
The whole year

Everything fits. Always.

All thirteen months share exactly the same structure. Intercalary days preserve the weekly cycle.

COMMON YEAR

January01

SMTWTFS
12345678910111213141516171819202122232425262728

February02

SMTWTFS
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March03

SMTWTFS
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April04

SMTWTFS
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May05

SMTWTFS
12345678910111213141516171819202122232425262728

June06

SMTWTFS
12345678910111213141516171819202122232425262728

Sol07

SMTWTFS
12345678910111213141516171819202122232425262728

July08

SMTWTFS
12345678910111213141516171819202122232425262728

August09

SMTWTFS
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September10

SMTWTFS
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October11

SMTWTFS
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November12

SMTWTFS
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December13

SMTWTFS
12345678910111213141516171819202122232425262728
Open visual toolkit

Turn a regular calendar into clear data.

Explore four real visualizations generated by @fixedcalendar/charts. The same accessible SVG works in React, Vue, static sites, server rendering, and Node.js.

Year calendarThirteen months of twenty-eight days for 2026, including intercalary days.2026COMMON YEARJanuarySunMonTueWedThuFriSat12345678910111213141516171819202122232425262728FebruarySunMonTueWedThuFriSat12345678910111213141516171819202122232425262728MarchSunMonTueWedThuFriSat12345678910111213141516171819202122232425262728AprilSunMonTueWedThuFriSat12345678910111213141516171819202122232425262728MaySunMonTueWedThuFriSat12345678910111213141516171819202122232425262728JuneSunMonTueWedThuFriSat12345678910111213141516171819202122232425262728SolSunMonTueWedThuFriSat12345678910111213141516171819202122232425262728JulySunMonTueWedThuFriSat12345678910111213141516171819202122232425262728AugustSunMonTueWedThuFriSat12345678910111213141516171819202122232425262728SeptemberSunMonTueWedThuFriSat12345678910111213141516171819202122232425262728OctoberSunMonTueWedThuFriSat12345678910111213141516171819202122232425262728NovemberSunMonTueWedThuFriSat12345678910111213141516171819202122232425262728DecemberSunMonTueWedThuFriSat12345678910111213141516171819202122232425262728Outside the weekYear Day
@fixedcalendar/chartsFramework-independent · Accessible SVG · MIT licensed
View on npm ↗GitHub ↗
Why try it

Less irregularity. More clarity.

[ 4×7 ]

Fair comparisons

Every month has the same number of weeks and weekends—ideal for analysis and planning.

[ = ]

Memorable dates

A date always falls on the same weekday. Learn it once, use it forever.

[ 13 ]

Open design

We are not asking to replace anything tomorrow. We build tools to experiment in parallel.

Hard questions

Criticism welcome.

Doesn't it break the continuous week?+

Yes. Intercalary days sit outside the week, an important objection for some religious traditions. We present it transparently and explore the calendar as a parallel system, not an imposition.

What happens to birthdays and contracts?+

Every date has an unambiguous Gregorian equivalent. Conversion tools support both systems during any experiment.

Do the seasons change?+

No. The year retains Gregorian length and leap-year rules; only the grouping of days changes.

Community-built

Three projects. Many ways to contribute.

Fixed Calendar is MIT-licensed free software. Improve the website, evolve the core engine, or build new ways to visualize time.

01 · Website

Improve how people discover the calendar.

Contribute content, translations, design, accessibility, performance, and responsive improvements.

  • Content and translations
  • Design and accessibility
  • Performance and documentation
Website repository ↗How to contribute
02 · Core library

Build the foundation for new tools.

Help with conversions, date validation, TypeScript types, tests, and integrations.

  • Algorithms and edge cases
  • Tests and TypeScript types
  • Adapters and integrations
Core repository ↗npm
03 · Charts library

Make calendar data visible.

Create accessible visualizations, themes, examples, and integrations for any framework.

  • New chart types
  • Themes and accessibility
  • Framework examples
Charts repository ↗npm
# Contribute to the website
git clone https://github.com/fixedcalendar/website.git
cd website
npm install
npm run dev
# Use the core library
npm install @fixedcalendar/core

# Explore and suggest improvements
github.com/fixedcalendar/core ↗