It is not my calculator. When I started mining about two weeks ago, I wish I knew as much as I do now. I'm just warning to be prepared for a more realistic payback time frame on graphic cards. I made the same kind of assumptions that ZeroShift made. But it is not a simple straight line calculation. And there are random factors in the exchange rate and the rate of difficulty increase. But I do agree that everyone needs to do their own  analysis of their investment/costs, risks, rewards. And in future, gusti, I will keep my mouth shut and not advise others of anything to do with mining. The only reason I joined this forum was to payforward what I had learned from it.