I have about $60 worth of Steem Power in my account, earned 100% from my previous posts over the last 2 weeks. Every upvote I make is $0.04. If I post once a day, I will earn $1.20 from my own upvotes in 30 days. It will roughly take me 4 years to double my SP. I don't know how @jerrybanfield could be doubling his SP in 180 days because his calculations look valid too.