Depends...
1. Do you scuff your tip often? Obviously, scuffing your tip wears it away.
2. Do you chalk every shot? Chalk is very abrasive and will eat away your tip even if you never scuff it.
3. What kind of tip is it? Softer tips wear away faster than hard tips. Also, some tip brands glaze over and need to be scuffed more often.
4. How often do you play?
All things being equal, I think you should get be able to get a couple years out of a new tip. But, some players have had the same tip on their cue for 15 years, and some players grind their tips away and need 4 tip replacements a year (yeah, I'm talking about you, Chad!).
Personally, I prefer a Moori III (M) and replace my tip every year whether it's worn down or not. Also, on my second shaft, I test damn near every new tip that comes out on the market (cuz you never know what the next "gotta have it" tip is gonna be). I'm lucky if those last a month before swapping out for a different "new" tip.