No, punching in 12x12 gives you a 13x13" frame:
Customizing a frame to fit a 12.0" x 12.0" print
13 x 13 x 0.75" Black Maple frame with No mat
and Standard glaze. $43.50
I'm saying that my matted print is 12x12 (or whatever), and I don't want to futz with making the numbers come out right.