Family Loan Limits to Avoid Interest

What is the allowed amount for a loan between family members in order to not have to pay interest? Is it exactly $10,000 per year? Do you need to immediately start making monthly payments back or set up a contract that just defines the terms of when repayment begins? It sounds like this is no really on the IRS' radar as long as it's $10k and below, so I just want to be clear about the amount allowed, no interest and repayment. Thanks

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