Amends existing law to revise provisions regarding computing Idaho taxable income of multistate or unitary corporations.

This bill relates to the taxation of multistate business income in Idaho. Over the past few decades, most states have moved towards taxing multistate income based on both market-based and single-sales factor approaches. Idaho currently taxes multistate income for sales other than tangible property (ie., intangible property and services) using a "cost-of-performance" method. Cost-of-performance assigns the sales revenue to the location having the greater proportion of services performed. Market-based sourcing assigns the sales revenue to the location receiving or benefiting from the services. Changing to "market-based" sourcing for these activities will create uniformity with other states. Note that Idaho currently applies market-based sourcing to the sale of tangible property which is already uniform to other states. Idaho currently taxes multistate income using a three-factor method to apportion business income, which includes: 1) Property; 2) Payroll; and 3) Double-weighted sales. Changing to a single-sales factor to apportion income will simplify the process and also create uniformity with other states. As other states have moved away from cost-of-performance as well as three-factor apportionment methodologies, instances of double taxation for Idaho-based companies, and instances of out-of-state companies doing business in Idaho without paying income taxes have become more and more prevalent. This bill resolves these two problems, provides for a more-favorable tax environment for Idaho, and simplifies the taxation of multistate income for both taxpayers and the State Tax Commission.