GIM stands for Gross Income Multiplier, which is also known as Gross Rent Multiplier (GRM). This is a method used to value plexes/apartments by dividing the price of the property by the current rental income. If the total current rental income is $20,000 and the asking price is $240,000 then the gross income multiplier =12. ($240,000 divided by $20,000 = 12.)