Don't use that calculator, to me its a joke. It was probably created by someone from Butterfly labs just to keep their customers from lynching them. I use this calculator which is far more accurate:
http://mining.thegenesisblock.com/a/103f27233bI have the inputs of the selected KNC miner and numbers starting from November which you can change the month. The difficulty value will automatically change as well. Have a look and have fun with it.
You can choose any current miner and it will automatically input their credentials into the calculator.