1099-INT Box 9: Private activity bond interest

How Box 9 works

Box 9 identifies the portion of a payer's exempt-interest payments — already included in Box 8 — that comes from specified private activity bonds, generally bonds meeting the private-activity-bond definition and, per the instructions, typically issued after August 7, 1986. Box 9 is a subset of Box 8, not an addition to it, so a payer reporting an amount in Box 9 should also show at least that much in Box 8 for the same year.

Because Box 9 is meant to already be counted inside Box 8, check that the two numbers line up in your own records — if Box 9 is populated but Box 8 looks too small or is blank, it's worth confirming with the payer's supplemental statement rather than assuming the form as issued is correct. Private activity bonds finance specific projects — certain housing developments, airports, or other facility financing — rather than general government operations, which is part of why the tax code singles out their interest for different treatment than ordinary municipal bond interest, even though both are federally tax-exempt for regular tax purposes.

The main consequence of a populated Box 9 shows up on the alternative minimum tax side, where the instructions point recipients to the Form 6251 instructions: private activity bond interest is a preference item that can increase alternative minimum taxable income even though the same interest is excluded from regular federal taxable income. A blank or zero Box 9 alongside a populated Box 8 simply means the payer's tax-exempt interest for the year didn't include this bond category — it isn't an error or an omission. Don't assume every bond described elsewhere as a private activity bond produces a Box 9 amount on your specific form; the box only captures interest the payer has identified as meeting the specified definition.