I typically have a 4-5 month break with little cycling between seasons so when I start my training I've dropped off quite a bit. And during the 1st 4 weeks my ftp typically jumps right around 10%. After that, provided I train smart, it continues to climb but each 4 week jump will be less.

Here is a chart out of the Coggans book "Racing and training with a power meter". It is a guess, as plenty of people are at each level with more or less, and for level my FTP is a higher than the listing while my 5 Second is low. But it should give you a rough idea of where people are at: