Hi Lilly! I'm new to wikitree..but I understand what your question is. Most Native Americans would not be saying, "I'm 18% Native American"...they break it down like this...full blood, 3/4 blood, 1/2 blood, 1/4 blood, 1/8th, 1/16th, 1/32nd...after that, you can say you have a drop of Native American in you, and if you are of the Cherokee people, even that drop counts. According to your 18% on your dna test, you can consider yourself 1/4 blood! My great grandmother was full blood Cherokee, my grandfather 1/2, my dad 1/4, and I am 1/8th. I hope this answered your question.
Sincerely, Kay Leclair