The Raspberry Pi comes without a real time clock. The official FAQ says so and we have to go with it, although on the forums many people complain and want a RTC added to the Raspberry. Well, there is no reason to do so. There are lots of free connections on the Raspberry that could be used to connect a clock. And hey, that is where the fun starts, anyway.
Do I need an RTC?
Well, that depends. So in most cases a plain “No” would be the correct answer. If you have your Raspberry connected to a network all the time and this network has access to the internet there is absolutely no reason (apart from the tinkering fun) to add an RTC. The Raspberry uses NTP, the Network Time Protocol, the get the correct time from the internet. Every time the Raspberry boots, the time is set.