The Iæran Calendar is a solar calendar that is the worldwide standard for determining the position of the Sun relative to the stars on Iær. The calendar year consists of 360 days, however Iær completes an orbit of its Sun in 360.3212 days. This results in the addition of a leap day typically every three years, and rarely in the fourth year.
Each year is divided into fifteen months, each with 24 days, totalling 360 days; the leap day is added to the middle (8th) month during a leap year, making a 25-day month in a 361-day year. The months' names follow a set order in the first seven months of the year; this order is essentially repeated (using a different prefix) in the final 7 months of the year. These traditions originated based on semi-annual harvests.
Each month is divided into three eight-day weeks, with the first day of the month falling on the first weekday and the last day of the month falling on the last weekday. When a leap day is inserted, it is placed in the middle of Minose's second week, effectively becoming the middle day of that week, month, and year all at once. This also makes Minose's middle week a nine-day week during a leap year, which ensures that the last day of the month falls on the last weekday as always.
While the standard week follows the same weekday name order, an inserted leap day has its own weekday name (Interdi), which is never otherwise used. The following table describes the weekday names: For Weekday below, the first number listed (not in parentheses) indicates the weekday's number during weeks that don't contain a leap day (over 99% of all weeks), while numbers in parentheses indicate that weekday's number during a week in which a leap day is inserted.