This is quite funny. My parents charged me $350 monthly rent when I turned 18. I worked at a Burger stopnchop for minimum wage. I wasn’t able to get that job until after I graduated because my parents forced me to babysit my brother for free. This put a huge pressure on me as a young adult trying to get my shit together. I was barely making any money, expected to pay nearly half of my parents rent while also saving for my own place. I ended up having to move out into what literally seemed like a trap house just to catch a break. I personally think that if you are going to charge your kid rent, you need to consider several things like; how much money do they make at their job? How much can you realistically expect them to save while they are paying rent? How old are they? Are they just finishing school? why are you charging rent? Is it to be spiteful? Is it because they refuse to get off their lazy ass? Is it because you are personally struggling? Have you considered other options? Such as sitting down with your child to have an adult conversation (since you want to treat them as an adult in other senses) and deciding together what a reasonable contribution to the household would be— based on their room size in comparison to the rest of the house, how much utilities they use, how much food they eat that you pay for, and what they can afford to contribute while also putting money back for their own house/apartment. Please do not do to your child what my parents did. I had to move out quickly just to be able to live. I had no time to save up ‘cushion’ money, so when my job temporarily shut down to be renovated, I was left with absolutely no money and got evicted. Please remember that this is your child. You are responsibile for them and just because they are 18 now, you should not forget that fact. They still need your help and your guidance. I suggest before charging rent, to tell them you would like them to move out. Give them 6–12 months to save money for this… and help them to find a home they can afford that is actually livable. Do not take advantage of your children. They are not a friend who asked to crash for a bit and never left. They are a being that you brought into this world. That you chose to take responsibility for and raise. Do not expect that just because they are 18 they should ‘carry their weight’ when they have never done so before. Help your child to transition into the real world and help them do so smoothly.