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 derived from the average year of the lunar and the solar: + 354.3829 /2 = 719.6254/2 = 359.8127 days, rounding to 360.
A 360-day year consists of 12 months of 30 days each, so to derive such a calendar from the standard Gregorian calendar, certain days are skipped.
For example, the 27th of June would be the 4th of July in the USA.
Ancient Calendars
Ancient calendars around the world initially used a 360-day calendar.Rome
According to Plutarch's Parallel Lives Romans initially used a calendar which had 360 days, with varying length of months. However, Macrobius' Saturnalia and Censorinus' The Birthday Book, claim that the original Roman calendar had 304 days split into 10 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.Egypt
Ancient Egyptians also used a 360-day calendar. One myth tells of how the extra 5 days were added.Financial use
A duration is calculated as an integral number of days between startdate A and enddate B. The difference in years, months and days are usually calculated separately:There are several methods commonly available which differ in the way that they handle the cases where the months are not 30 days long, i.e. how they adjust dates:
European method (30E/360)
Source:US/NASD">Financial Industry Regulatory Authority">NASD method (30US/360)
Source:[International [Swaps and Derivatives Association|ISDA]] method
Sources:BMA">Bond Market Association">BMA/PSA">Public Securities Association">PSA method
Source:Alternative European method (30E+/360)
Sources:| Package | Function | Variant |
| Apache OpenOffice, Collabora Online, LibreOffice and Microsoft Excel | DAYS360 | NASD, but not SIA-compliant |
| Apache OpenOffice, Collabora Online, LibreOffice and Microsoft Excel | DAYS360 | European |
| Apache OpenOffice, Collabora Online, LibreOffice and Microsoft Excel | YEARFRAC | NASD and European |
| SQL Server 2000 Analysis Services | Days360 | |
| Mathworks Financial Toolbox | days360 | US/NASD |
| Mathworks Financial Toolbox | days360e | European |
| Mathworks Financial Toolbox | days360isda | ISDA |
| Mathworks Financial Toolbox | days360psa | PSA |
| Gnumeric | DAYS360 | |
| Apple Numbers | DAYS360 | NASD and European |
| Apple Numbers | YEARFRAC | NASD and European |