It's a tricky thing. I'm 19 years old and I completely understand your approach to the matter of labeling yourself as an independent. The reason why you can't is because of the fact that you rely on your mother to assist you in paying for college. In the FAFSA, you need your parent(s) to help file it cause the government goes through a myriad of ways to find out if you can afford college. To call yourself independent would mean that your pay your own health insurance, pay for your own place to stay and/or you pay to live on campus, and you possess enough credit to receive loans. End of it all, to claim as independent you must receive no support from your parents what so ever. Now don't let the concept of being dependent though bring you down. Since you do not have any ties attached to you being a dependent, use this time to increase your credit score, create a savings account, invest into your future, and get yourself financially ready for when you're independent!
