Plus, if you notice, there's a progression here. You have 1 point per increase for 11, 12 and 13. Then it's 2 points per increase for 14, 15, and 16, going up to 3 for 17 and 5 for 18. So following this progression (+1 per point after 16) we get the following...
19 = 21 points
20 = 27 points...