Always buy a little more than you need!
You don’t want to run short.
Dye lots may vary.
You may make a mistake (or even change your mind about a particular fabric once you have started and decide you want to use more than you originally planned). When this happens, it is almost 100% certain that if you go back for more they will tell you they just sold the last piece!!! The internet helps…you can often track down more, but you may have to wait several days for it to arrive and pay extra for shipping (and then there's that dye lot issue!).
And, of course, whatever you don't use in this quilt goes into your stash and becomes FREE fabric for another one down the line!