I shortcut leaving 3 inches all around a queen size quilt once and thought I could keep it from shifting as I stabilized it by STID around the blocks. In the end one end shifted back about 1.5 inches and I had to piece in a section of batting and a section of backing. This was far more trouble than if I had left the proper perimeter to start with. When I completed my repair job an onlooker could not see it but it was sure a lot of extra work. It will never happen to me again. Be safe and use a bit of a safety margin and use the scrap for a scrap quilt.

Not really having anything to do with the subject but when grand daughter & I have to piece pieces of batting together for a project we call it "Frankensteining" lol, good for a laugh at the pain in the patooty work.:D

I give myself at least 4 inches Like other have said one screw up and you'll wish you have not c
heaped out.

I am always very frugal and occasionally skimp, but clearly it is better to cover your backside. What I have discovered is that if I have extra around the edges, once it's cut off it's great to use for binding on another quilt. So having a good 2" all around is actually less wasteful. Better to be safe than sorry. I have a Sweet Sixteen and rarely have much shifting. I would hate to have to add the large amounts needed for long arm setup, though. Fabric is just too expensive!

Alittle extra is best and yuou could baste around the edges

I like 2"-2 1/2", but I have worked with much less if that's the way the back turned out. No problem with shifting at all, but I did miss having something to grab when FMQ the border.