Developer API
Convert any date both ways with a simple REST call, including holidays per country.
The Equinox Calendar divides the year into 13 months of exactly 28 days, keeps the 7-day week, and gives the 365th day to the whole world. The year still starts on 1 January, so nothing has to change overnight.
Free and openAn open standard with free tools: converter, API, .ics subscription and printable calendar.
Pick any date to see it in the Equinox Calendar. Every month looks exactly like this one, and starts on the same weekday.
13 months \u00d7 28 days = 364 days. Day 365 is World Day, outside the week. Every four years, a Leap Day, also outside the week. The year starts on 1 January, as it does today.
Thirteen months, four weeks each, one World Day.
Show Equinox dates next to the calendar you already use.
Use the open API and toolkit in your own products.
Uneven months make planning harder for finance, education and logistics. A fixed calendar makes every year the same, without moving New Year.
Because every month is exactly four weeks, every date falls on the same weekday, every year.
Thursday 25 Lucien, every year.
Calendar reform happens in phases: first understanding, then tools, then dual display, and only then standardisation.
Launch site, whitepaper and open tools
API, .ics exports and app integrations
Adoption in finance, HR, education and government
UN/ISO proposal and voluntary global adoption
An open REST API and reference libraries under MIT and Apache 2.0, so any app can show Equinox dates.
{
"gregorian": "2026-04-27",
"equinox": {
"year": 2026,
"month": "Solis",
"day": 5,
"weekday": "Friday"
},
"is_holiday": true,
"holiday_name": "King's Day (NL)"
}Convert any date both ways with a simple REST call, including holidays per country.
Subscribe to Equinox dates next to your normal calendar in Apple Calendar, Google Calendar or Outlook.
Thirteen identical months on one sheet. Print it once; it's valid every year.
Managed by a non-profit foundation. Reference implementations under MIT and Apache 2.0.
The standard is managed by a non-profit foundation, not a company.
Reference implementations under MIT and Apache 2.0.
The year still starts on 1 January and the 7-day week stays intact.
Dual display first. Nobody has to switch until it's useful to them.
Every year I re-learn which months have 31 days, and every year my birthday falls on a different weekday. None of that is necessary.
The Equinox Calendar is my proposal for something better: equal months, perfect weeks, and one day each year for the world itself.
No. The civil year still starts on 1 January, so the transition is seamless for existing systems.
13 × 28 = 364 days. The 365th day, at the end of the year, is World Day: a universal holiday that isn't part of any week.
Every four years a Leap Day is added. Like World Day, it sits outside the week, so the weekly cycle of dates is never disturbed.
Yes, deliberately. It's what makes every date fall on the same weekday forever, and it gives the world one shared holiday.
Nobody. It's an open standard managed by a non-profit foundation, with reference implementations under MIT and Apache 2.0.
Free whitepaper, calendar subscription and API access.