I've never actually calculated the angle. It just "is what it is"... and I really dislike that phrase. But, in this case, it's true. What I do calculate is the neck width at the nut, the last fret and at the bridge. OK, so it's more like the spread at the bridge, and the nut, then connect the dots. I use the fret2find utility to calculate string spacing, overhang, etc. Then I print that out, or draw it out using the dimensions.
Once I have the outline, I draw in the laminates, keeping the outermost lams parallel to the outside edge. The center laminate is straight and parallel with itself. What's leftover is two angled laminates. You could leave out the straight center lam, or add more parallel lams on the outside and end up with one single tapered center lam if you want.
So, to actually make the pieces, I measure the taper in a couple of spots on the drawing, ( at the nut, and scale length) and use those measurements to make my pieces. I don't know what the angle is, cuz it doesn't matter.
Cutting them is a bit fiddly. You can use a taper jig with a table saw, or with a band saw for that matter. I laid mine out on straight grained maple trying to keep run-out to a minimum, then freehand cut them on the band saw. (I make them larger than I need to) Then I trued up one side of each piece with a hand plane. I glued those two faces together using the tape/CA trick. I then roughly true up one outside face and ran them through the drum sander... flipping as needed. That's probably tough to get a mental picture of what I'm talking about. I'll see if I can find pictures to post.