If I am a guarantor of my son's student loan an I made the payments can I deduct the interest?

[AlanT]

Yes, you can deduct the interest you paid during the year on a qualified student loan used to pay for tuition, fees, room and board, books and supplies for yourself, your spouse, or your dependent is deductible. This includes both required and voluntarily pre-paid interest payments.

As long as you are legally obligated to pay the loans, you can take the deduction.  Being a guarantor makes you legally obligated. 

Complete Qualifications:

You can claim the deduction if all of the following apply:

• You paid interest on a qualified student loan in tax year 2018;
• You can take the deduction as a student, or as a parent making payments on your dependent student’s loan. However, you or your spouse, if filing jointly, can't be claimed as dependents on someone else's return.
• You're legally obligated to pay interest on a qualified student loan;
• Your filing status isn't married filing separately; and
• Your MAGI is less than a specified amount, which is set annually.