Yestarë, in the calendars of the Elves and the Númenóreans (this calendar was actually derived from that of the Elves), was the name for the first day of the year. It meant literally, in Quenya, 'First Day'.

The actual date of Yestarë was different in some of the calendars. In the Reckoning of Rivendell it would have fallen on our modern day 28th of March. In the calendar of the Númenóreans, it would have corresponded to our 22nd of December.