17.5 neck on my dress shirts with an athletic build. Just got the shirt from A Cut Above; the neck fits just fine but I can't get the main part of the shirt to button across my shoulders/chest. It's the tapered version. Looks like even with the large neck size it assumes a very slender build up top - not talking about the gut, rather increased upper body size from weightlifting. Going to try an 18.5 and see if I can get it altered (which is a full size above what I normally wear). Other than that I like the shirt.