The IRS requires that a minimum rate of interest be charged on loans. If you do not charge at least the minimum rate, the IRS will still require you to pay tax on the difference between the interest you should have charged and what you actually charged. If these excess amounts become large, or if the loan is forgiven, there may also be gift tax implications.
There are some exceptions, though. Loans of up to $10,000 generally can be made at a lower (or zero) rate of interest, as long as the proceeds aren’t invested. Loans between $10,001 and $100,000 are exempt from the minimum interest requirement as well, as long as the borrower’s investment income is $1,000 or less. If the investment income exceeds $1,000, you’ll be taxed on the lesser of this income or the minimum IRS interest.