http://www.apple.com/batteries will give you a more accurate indication of how your battery usage ought to be.
Using the right charger for your Mac is critical to getting the right amount of charge.
If you are using the charger that came with your Mac, and it shows no sign of fraying, and you aren't attaching an external peripherals to the Mac outside of power, you should get the advertised range of length of charge at least for the first year. Some variables such as power surges, the wrong power adapter, or power strip, or old electrical circuits can all affect charge. I do not recommend traveling with the computer without shutting it down first. The computer can due to background programs find itself turning its screen on, if it was not shut down, if the right application tries to turn on. This will rapidly reduce the battery charge.
High end graphics programs such as games or videos will also accelerate charge loss.
Your computer is typically under a 1 year hardware warranty from Apple. Check your support options on http://checkcoverage.apple.com/