Traditionally Otsukimi or the moon-viewing event is held on August 15th based on the old lunar calendar. But it actually falls on different dates depending on the year since we use the solar calendar now. This year, 2018, Otsukimi falls on September 24th. The full moon is actually the 25th. Obviously, the lunar calendar is based on the moon, so 15th of each month is supposed to be the full moon. However, the calendar is not perfect, and in some months a 1~2 day gap can occur.
