We use a rolling average of 730 calendar days.  That would include 2 years of leagues and tournaments.

Events are weighted differently:
All leagues are 100%
All tournaments except majors are 150%
All major are 200%

Example:
ABDA Nationals
You played 24 games and scored 864 points
In the adjusted average, it would count as 48 games and 1728 points

Stats over 730 automatically come off your average.

Majors include:
ABDA Nationals
PA States
Battle of the Bars