根据 IRS 说法，以下的 interest 是不收税的
U.S. Source Interest Income that is not connected with a U.S. trade or business is excluded from income if it is from:
- Deposits (including certificates of deposit) with persons in the banking business,
- Deposits or withdrawable accounts with mutual savings banks, cooperative banks, credit unions, domestic building and loan associations, and other savings institutions chartered and supervised as savings and loan or similar associations under federal or state law (if the interest paid or credited can be deducted by the association),
- Amounts held by an insurance company under an agreement to pay interest on them,
- Interest on obligations of a state or political subdivision, the District of Columbia, or a U.S. possession, generally is not included in income. However, interest on certain private activity bonds, arbitrage bonds, and certain bonds not in registered form is included in income, or
- U.S. source interest income that is not connected with a U.S. trade or business and that is portfolio interest on obligations issued after July 18, 1984, in registered form is excluded from income. For a discussion of portfolio interest, refer to “Portfolio interest exempt from chapter 3 withholding” in Publication 515, Withholding of Tax on Nonresident Aliens and Foreign Entities.
IRS refund 里的 interest 似乎不符合以上任何一项，这么说起来可能要缴税?不过不知道要填在 1040NR 的哪里，税率又是多少？