In general, it limits a taxpayer’s interest expense deductions for a taxable year to the sum of 30 percent of adjusted taxable income (ATI) and its business interest income. Certain taxpayers involved in the sale of motor vehicles may also be able to increase their section 163 (j) limitation by any floor plan financing interest expense.

Under section 163 (j) (1), the amount allowed as a deduction for BIE is limited to the sum of (1) the taxpayer's business interest income (BII) for the taxable year; (2) 30 percent of the taxpayer's adjusted taxable income (ATI) for the taxable year (30 percent ATI limitation); and (3) the taxpayer's floor plan financing interest expense for the taxable year (in sum, the section 163 (j) limitation).

If section 163(j) applies to you, the business interest expense deduction allowed for the tax year is limited to the sum of: 1. Business interest income, 2. 30% of the adjusted taxable income, and 3. Floor plan financing interest expense. Carryforward of disallowed business interest.

Section 163 (j) limits the deduction of business interest to the sum of a taxpayer’s business interest income, floor plan financing interest, and 30% of its ATI for a given taxable year. The CARES Act modified the limitation to 50% of ATI for tax years beginning in 2019 and 2020 (partnerships have special rules).

The Sec. 163 (j) limitation applies to any interest properly allocable to a trade or business. For corporations that are partners in a partnership (or members of a limited liability company (LLC) taxed as a partnership), the limitation applies first at the partnership level and again at the partner and shareholder level.