If you did 12 miles each way 4x week, you should be able to do 20. I used to ride 36 miles round trip every day year round ( except hard rain and snow). Averaged 4 days a week. I did this for years until a job change made it impossible. Most important is you have a safe route. Mine was neighborhood roads and bike path, then about 1mile in city. Pace yourself, don’t get in a race with other riders or you’ll be wiped out by Friday. Full fenders. Separate pair of shorts for the ride home. I loved it, will try to start again when I go back to the office.