From Tolkien Gateway

Loëndë was also known, especially by the Hobbits, as Mid-year's Day. Loëndë was the day that fell in the middle of the year in many of the calendars of Middle-earth. Since Mid-year's Day in the Shire Calendar was intended to correspond with the summer solstice, then this should apply to loëndë in the Kings' Reckoning and Stewards' Reckoning calendars of Gondor as well. In the New Reckoning, loëndë corresponded with 24 September in the Shire Calendar.[1]

See also: Mid-year's Day
See also: Enderi