well then you need to go buy an accounting book and read it!
No wonder you barely make any money...
http://en.wikipedia.org/wiki/Return_on_investment and any other fucking accounting book said:(Vf-Vi)/Vi where Vf = final amount and Vi = initial amount
Start with $1, double your money, $2 in. Vi=$1, Vf=$2... (2-1)/1 = 1.. = 100%.