Box 20 · code N
K-1 box 20 code N: business interest and where it stops
N does not stand alone. Business interest expense is limited at the partner, and the two letters that measure it — excess taxable income and excess business interest income — sit on the same page beside it.
The wording on the form is: Business interest expense (BIE). Read against the year printed in the K-1 header, because the letters are reassigned between years.
Where the letter goes
Form 8990, where the section 163(j) limitation is computed, with any disallowed amount carried forward at the partner level.
The deduction is limited to business interest income plus a share of adjusted taxable income. That share comes from the partnership as excess taxable income, which is why N without AE and AF is not a number anyone can act on.
What has to be true before any of it can be claimed
- AE and AF are read with N. Excess taxable income raises the ceiling and excess business interest income is part of it; a worksheet that records only N has recorded the numerator and thrown away the denominator.
- The partner's own business interest is in the computation. A partner with borrowing outside the partnership has items the K-1 cannot see.
- The disallowed part is carried forward. Section 163(j) defers rather than destroys, and the carryforward is a partner-level balance that has to be maintained.
What the statement has to show
N, AE and AF normally print amounts. The set is short enough to sit in one row of a worksheet, and it should, because separating them is how the limitation gets computed from half the inputs.
What goes wrong, and the shape of it
- N claimed in full. The K-1 figure is the expense, not the deduction. Entering it as deductible is the failure this letter is designed to prevent.
- AE and AF left on the page. They are what makes N usable. A row that carries N alone cannot support the computation and will be recomputed from scratch by whoever reviews it.
- The carryforward treated as an expense of the new year. A carried-forward disallowed amount is claimed when there is capacity, not automatically at the start of the next season.
What the reading step does here, and what it does not
K1 FastTax reads N, AE and AF as three separate letters with their own amounts and pages. It does not compute the section 163(j) limitation.
The rest of box 20 is in the full box 20 code list , and the printed wording of the box itself is on the box 20 page . This page describes where a code goes; it is not tax advice, and the Partner's Instructions for the year on your K-1 are the authority.
Plain answers
Questions about box 20 code N
What is K-1 box 20 code N?
Business interest expense. It is the partner's share of business interest the partnership could not deduct at its own level, and it is subject to the section 163(j) limitation again in the partner's hands.
Why do codes AE and AF matter when I have N?
They are the other half of the limitation. AE is excess taxable income and AF is excess business interest income; without them the amount in N cannot be tested against anything.
Is business interest expense deductible in full this year?
Not automatically. The limitation is computed on the partner's return using the partner's own business interest income and the allocated excess taxable income, and whatever is disallowed carries forward.
Can a K-1 carry N without AE or AF?
It can print them blank, and blank is a fact worth recording rather than filling in. A blank AE is not the same as an AE of zero, and treating them the same changes the computation.
Read box 20 code N from your own K-1
K1 FastTax keeps the letter, the amount and the page together, keeps a statement reference as STMT rather than zero, and records which rows a person checked.