Based on our understanding you need approximately 3500 points to obtain a 20 year letter. See attached documentation.
Finding Your Points
In order to receive a 20 year letter (which implies you want to know when you have a vested retirement with the Guard or Reserve), an Army Reserve or National Guard soldier needs 20 good years of service. The can be a combination of Active Duty, Guard and Reserve time.
A “good year” is considered to be a minimum of 50 points during a given year. Or, a “good year” is one year on active duty.