GPU mining is not profitable if you have to buy a GPU because the cost of the GPU is more than it will ever earn. In this case it is better to buy the bitcoins outright than to try to mine them with a GPU.

For those that already have a GPU, mining is only profitable as long as the revenue from mining is greater than the cost of power. Your profit depends on the difficulty and the price of BTC.

For example, if your electricity costs $0.10/kWh and your GPU uses 250W then your power cost is $0.60 (or about 0.0060 BTC) per day. If your GPU's hash rate is 600 MH/s, then it currently mines about 0.0072 BTC per day, and your profit is 0.0012 BTC (or about $0.12) per day.


Go to http://mining.thegenesisblock.com/ for more accurate calculations.