For tax years beginning after Dec. 31, 2017, deductions for business interest expense is generally limited to the sum of a taxpayer’s business interest income, 30 percent of adjusted taxable income and floor plan financing interest. 

This limit does not apply to taxpayers with average annual gross receipts of $25 million or less for three prior tax years. Annual adjustments will be made to the amount for inflation starting in 2019.  Amounts will be calculated and reported on new Form 8990, Limitation on Business Interest Expense Under Section 163(j).

Also excluded the limits are businesses, including performing services as an employee, electing real property trades or businesses, electing farming businesses and certain regulated public utilities. Taxpayers must elect to exempt a real property trade or business or a farming business from this limit.