Revenue and taxation; income tax; adjustments; retirement benefits; effective date.

HB 1391 amends Oklahoma's tax calculation rules for income tax purposes. It adjusts how taxable income is calculated by adding interest from state/local obligations (unless already exempt), deducting amounts the state can't tax due to federal or constitutional limits, and changing how businesses handle federal net operating loss carryovers. The bill also clarifies how income from property (like real estate or investments) and business activities should be allocated between Oklahoma and other states. This affects businesses and individuals with multi-state income, particularly those with operations across state lines or investments in out-of-state property. The changes align Oklahoma's tax rules more closely with federal calculations for specific scenarios.