比如在加州, http://oag.ca.gov/consumers/general/usury
1. The California Constitution allows parties to contract for interest on a loan primarily for personal, family or household purposes at a rate not exceeding 10% per yea
2. In transactions for the purchase of goods or services which are not for personal, family or household purposes, there are normally no limits to finance charges except those set by the parties. 這個應該適用於你的情況,你是基本上是生意貸款(炒股),應該沒有高利貸限製。所以你不必因為內疚而不收利息。
當然,如果你不在加州,請自己google本地的法律。比如紐約的法律又不一樣 http://kdklaw.com/whats_new_02_private-loans.htm