Lending money to a cash-strapped friend or family member is a noble and generous offer that just might make a difference. But before you hand over the cash, you need to plan ahead to avoid tax complications for yourself down the road.

Take a look at this example: Let’s say you decide to loan $15,000 to your daughter who’s been out of work for over a year and is having difficulty keeping up with the mortgage payments on her condo. While you may be tempted to charge an interest rate of zero percent, you should resist the temptation.

Here’s why:

When you make an interest-free loan to someone, you will be subject to “below-market interest rules.” IRS rules state that you need to calculate imaginary interest payments from the borrower. These imaginary interest payments are then payable to you, and you will need to pay taxes on these interest payments when you file a tax return. To complicate matters further, if the imaginary interest payments exceed $16,000 for the year, there may be adverse gift and estate tax consequences.

Exception: The IRS lets you ignore the rules for small loans ($10,000 or less), as long as the aggregate loan amounts to a single borrower are less than $10,000, and the borrower doesn’t use the loan proceeds to buy or carry income-producing assets.

As was mentioned above, if you don’t charge any interest, or charge interest that is below market rate (more on this below), then the IRS might consider your loan a gift, especially if there is no formal documentation (i.e. written agreement with payment schedule), and you go to make a nonbusiness bad debt deduction if the borrower defaults on the loan or the IRS decides to audit you and decides your loan is really a gift.

Formal documentation generally refers to a written promissory note that includes the interest rate, a repayment schedule showing dates and amounts for all principal and interest, and security or collateral for the loan, such as a residence (see below). Make sure that all parties sign the note so that it’s legally binding.

As long as you charge an interest rate that is at least equal to the applicable federal rate (AFR) approved by the Internal Revenue Service, you can avoid tax complications and unfavorable tax consequences.

AFRs for term loans that is, loans with a defined repayment schedule, are updated monthly by the IRS and published in the IRS Bulletin. AFRs are based on the bond market, which changes frequently. For term loans, use the AFR published in the same month that you make the loan. The AFR is a fixed rate for the duration of the loan.

Any interest income that you make from the term loan is included on your Form 1040. In general, the borrower, who in this example is your daughter, cannot deduct interest paid, but there is one exception: if the loan is secured by her home, then the interest can be deducted as qualified residence interest–if the promissory note for the loan was secured by the residence