360-day calendar

The 360-day calendar is a method of measuring durations used in financial markets, in computer models, in ancient literature, and in prophetic literary genres. It is based on merging the three major calendar systems into one complex clock, with the 360-day year as the average year of the lunar and the solar: [365.2425 (solar) + 354.3829 (lunar)] = 719.61 ÷ 2 = 359.8 days rounded to 360. It is a simplification to a 360-day year, consisting of 12 months of 30 days each. To derive such a calendar from the standard Gregorian calendar, certain days are skipped.

Ancient Calendars

Ancient calendars around the world initially used a 360 day calendar.

Rome

Romans initially used a calendar which had 360 days, with varying length of months.

India

The Rig Veda describes a calendar with twelve months and 360 days.

Mesoamerica

In the Mayan Long Count Calendar, the equivalent of the year, the tun, was 360 days.

Financial use

A duration is calculated as an integral number of days between start date A and end date B. The difference in years, months and days are usually calculated separately: