I don't think there's any definitive answer for that question, it's completely dependent on what you're using on your phone. With heavy use (which is most of the time with me), I'll get 5-6 hours. Just in standby with the occasional email, text, and call, it should last all day.
With normal usage, I get 10-12 hours on most days. That includes some light web surfing and 5 hours of Pandora. On the weekends, when I'm home and not using my phone, it's usually 18-20 hours or more.
It depends on how much you use it, how bright you have the screen and how many features you have turned on that work while the phone is asleep. According to GSam, since July 26th I've averaged 24 hours of total time with 7 hours and 43 minutes "Active" and 2 hours and 16 minutes of screen on time.