This is not a question about margin. I am not structuring this as a survey or quiz, but I just think it might be an interesting discussion, to hear different views... If you could get an unsecured loan from a bank or some other lender--not a mortgage loan, but rather an unsecured loan that is structured a lot like a mortgage loan, e.g., monthly payments amortized over 20 or 30 years... How low would the interest rate have to be for you to be comfortable taking such a loan and using the money to trade? How much would you borrow? You may assume for this discussion that even though it is not a mortgage loan, you are nevertheless personally liable for repayment, and that you have some meaningful assets that would be subject to garnishment or attachment if you default on the loan. You may also assume that the loan is a genuine arms-length transaction from a disinterested lender, i.e., you are not borrowing the money from your brother-in-law, or any other type of arrangement that would create risk to family relationships, or other hard-to-quantify risks or variables.