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The calculator simply looks at the past, difficulty is exponentially increasing the calculator has never been accurate for long term. I have many many friends that made this exact mistake and lost much more than they ever made.

It might of course not be 100% accurate, but how can it be looking into the future?
Supposing some kind of exponential increase with the profit curve flattening out after a certain time is as good of a prediction as one can make.
I will break even fast, so I 'm not concerned about loosing "much" more than ever made...