Cutback weeks - how much? (Read 443 times)

I'm on a three week jag of mileage increases, and those are starting at the high point I reached just over 2 months ago before taking time off due to a newborn. I've never done a cutback week before; I just built my miles slowly. I'm still building quite slowly actually, but since it's a big increase from almost no miles just a few weeks ago, I figure my body could use a break. So, how much should I cut back next week? What's a good rule of thumb for cutback weeks?