Some people are uncomfortable charging their friends or family members interest for loans, but you may consider at least charging a bit since that money will not be able to work for you in other ways until it is paid back. You can charge whatever interest rate you want, but in general, most choose to charge a bit less than what a bank might charge for a personal loan. Many choose to charge between five and ten percent interest. Many states have usury laws that limit how much you can charge for interest. Even if it is a personal, private loan it is prudent to stay under the usury limit in case you end up in court for nonpayment in the future.