Since you are quoting the off-peak and on-peak rates, I would imagine you are not including all the fees, supply charges, and misc. BS that gets tacked on. My 9cents is bottom line > total bill divided by Kwh used. You can't do that with on and off peak setups.Here in my area in PA, we are roughly $.07/Kwh. I personally have a time of day meter and pay peak and non-peak rates, during the evening and weekends we pay $.04 at most and during the day we pay the $.07.
Moey beat me to it!