An Aiosi year takes three-hundred and fifty days as the planet traces its path around the parent star Thosanus, with each day lasting just over twenty-four hours (plus 0.0986 seconds).
The new year begins on the day of northern midsummer.
The Aiosi calendar consists of seven-day weeks:
An Aiosi month is thirty-five days (or five weeks) long, with each month name derived from a major event in the first year of the Old Vanguard's journey:
- Outset - The group depart Uris and the journey begins
- Dawnhunt - Landfall is made in Oro, and the first geomantic behemoth is slain. The Alchemist leads a suited family to drink from the corpse.
- Treestride - The Alchemist raises Sylvos and crowns the first of the elemental kings.
- Ocean's Ire - During a hurricane the water-wielding family of leviathans is slain and superceded by the Hydro line.
- Long Ascent - After the wind-warping ziz at the apex of Highhallow are hunted down, the Aero royal line is established.
- Dunemarch - After the routing of the dragons of Dos, the Pyro family is founded.
- Vast Night - With the three substance elemental houses under him, the Alchemist sets his sights on ensuring the loyalty of the Old Order, eventually subduing Erobias.
- Sunscorch - The last to fall in line, Athanon too succumbs to the might of the Alchemist's will.
- New Accord - Outside of Uris, the world is seemingly united under the Alchemist.
- Reformation - The Building and Breaking occurs.