Originally Posted by
m907
Somebody can correct me if my math is wrong, but there are 118 window and aisle seats on a Southwest 737-800. So everything up to B-58 is guaranteed a window or aisle seat, and since the A1-A15 slots often aren't completely filled and many passengers will sit together, anything up to the low C group will pretty much guarantee you won't get a middle seat on a 737-800 or MAX8.
Definitely depends on through passengers, preboards, and family boarding - but I agree that any B 'should' get an aisle or window nearly all the time on the -800/Max. Family boarding used to bite us pre-AList out of Orlando, and I've been on a few connecting flights where there were an unusual number of through passengers, but that wasn't particularly common.