MT HB412

Creates a property tax exemption for modifications that add living space to existing class four residential property, including increasing finished area or altering existing space

Exemption amount equals the lesser of the increased market value from the modification or 15% of the property's market value from the prior year

Modifications made within 3 years of new construction are ineligible, and only one exemption may be granted per property within a 6-year period

Exemption terminates upon sale of the property and is automatically granted by the Department of Revenue

Applies to property tax years beginning after December 31, 2025