If we use the data from penguinpablo the available supply went from 277.44 million to 326.19 million in one year which is an increase of 17.57%. Now this is not the inflation rate. To get the inflation rate we need to compare not the avaiable supply but the virtual supply from last year to this year. Unfortunately it doesn't seem that he is keeping track of that so I had to lookup the marketcap of SBD and the price at that time, then I converted it to the equivalent in steem and added it to the available supply from last year to get the virtual supply from back then.

The result is this: the virtual supply went from 293.74 million to 362.43 million which is a real inflation rate of 23.38%.

Note: the virtual supply from this year was obtained from steemworld.org and not by an estimation as I did for the number for a year ago. It's important to use the virtual supply to estimate the inflation rate because it represents both the the current supply of steem plus the amount of steem that can in theory be created by converting all the SBD to steem.