I am a baritone, and started trying to improve my range about a year ago. I do not receive any formal training, but I know the basics of what to do and not to do.
I warm up for about 15 minutes before attempting a song that requires me to get out of my comfort zone.
About a year ago when I started singing, my highest note was G above middle C, and this was a huge stretch.
Now, a year on, I can sing an A, one tone higher, but it is a stretch and I fatigue very quickly if I attempt this note, so tend to stay away from it.
I understand this is quite a vague question and everyone is different, but with formal training from a reasonable coach, daily practice, what is a realistic expectation for range improvement in say, 2 years time?