http://bitcoin.stackexchange.com/questions/8568/equation-for-mining-profit

общая идея

$ HashTime = ((поплавок) $ трудность) * (POW (2,0, 32) / ($ hashRate * 1000,0));
$ BlocksPerDay = (24,0 * 3600,0) / $ hashTime;
$ CoinsPerDay = $ blockCoins * $ blocksPerDay;
$ RevenuePerDay = $ coinsPerDay * $ ConversionRate;