The 'interest' on Steem Power is 9 out of every 10 new STEEM units being divided among people holding Steem Power, so the interest rate changes constantly. You can estimate your interest by writing down the number of Steem Power you have, waiting five minutes and refreshing the wallet page. You SP balance will have increased - if you subtract the two numbers and divide by 5 you get your interest rate in SP per minute.

STEEM dilution rate comes from the whitepaper (100% dilution per year).