If you tithed on your gross income then you have already tithed on your refund. Most people who tithe on their net income would tithe on their refund. Remember though that it's not what you have to give but rather want to give.

Pastor Mark has several tapes/cds that you should get a hold of that talk about New Testament giving.  Go to Calvary's Resource Ministry:  SM351, NU005, 1CR 381-382.

Listen to Pastor Mark's tapes, --you'll be blessed.

Jesus said, "If you give, you will receive. Your gift will return to you in full measure, pressed down, shaken together to make room for more, and running over. Whatever measure you use in giving--large or small--it will be used to measure what is given back to you." Luke 6:38 NLT