Nennali (Nehenni)

 January - Wolf Moon
February - Storm Moon
March - Carp Moon
 Sunborn (spring equinox)
April - Seed Moon
May - Goose Moon
 Wild Night (Beltaine)
June - Rose Moon
 Midsummer (summer solstice)
July - Mead Moon
August - Wort Moon
September - Barley Moon
 Coldborn (autumn equinox)
October - Blood Moon
 Dead's Night (Halloween)
November - Snow Moon
December - Hearth Moon
 Longnight (winter solstice)

Notes: this is the official calendar listed in Will of the Empress. In previous books, other months like "Sap Moon" are mentioned, but they seem to have been discarded to follow this calendar later on.

The week

 Sunsday
Moonsday
Starsday
Earthsday
Airsday
Firesday
Watersday

Birthdays:

Briar: twentieth Goose Moon
Tris: sometime in Wolf Moon
Rosethorn: Longnight. She celebrates at Midsummer instead.