The one you have works fine.  It gives the BTC est per day and they use per day for rental prices.  So I can put in 1 GH/TH/PH and see the rate. I was thinking it would be cool if we could enter the rate per day for rent instead of machine cost to see real time rental estimates.  It would probably need to be a separate calculator.  Like the same one, just revamped for renting.  So we could put in the speed we want to rent, rental length, and the rental rate.   Then get a good idea of what to expect.  I imagine there are a lot of people renting that know its a gamble, but really don't know the odds.  Its easy to feel like you are making money when its coming in renting, but in reality you are slowly losing money.  I have a feeling a lot of people are mining and renting who don't know that their margins are shrinking as a result.