If you want to get really technical, it is actually 9.5%, narrowing to 0.95% by 0.01% every 250,000 blocks (Roughly 0.5% per year). There is also a 'variable' aspect to it, because when SBD is converted to STEEM, it can be done above or below the market price that it was printed at.

Ignoring all the technicalities, 9% is a pretty good estimate :)