That's what I did but my number came out to be quite lower than I thought... I got like $116 for a 400 17/7 and two 600's 12/12 + fans. I'll have to check my calculations again.
I don't know about a calculator .
I have a 3 bedroom / 2 bathroom house .
I run a 600W HPS digital ballast and fans running 24/7
My electric bill has gone up about $25 .