Every year the National Park Service (NPS) offers entry into National Parks with no fee.  In 2022 the four days to look forward to at Glacier National Park are:

Saturday, April 16 
1st Day of National Park Week

Wednesday, August 4
The Great American Outdoors Act

Saturday, September 24
National Public Lands Day

Friday, November 11
Veterans Day

Normal fees for a 7 day pass are $35 per vehicle ($25 in winter), $20 for a visitor on foot or bicycle, $30 for motorcycle.  An Annual Pass is $70.  Passes can be purchased online.   Also, you still need to get a Reservation for days between May 27 and September 11, 2022 unless you already have a reservation (or activity) booked in the park for lodging, camping, transportation or a service which counts as your entry reservation.