I've underwritten enough apartment deals to know that the $300-per-unit reserve number on most proformas is fiction. Real numbers run $500 to $2,000, depending on the building, prior rehab, and prior upkeep. That gap compounds across sectors, and it's one of the biggest reasons some real estate business models produce more cash per dollar than others. Here's what 37 years of NCREIF data says about which ones.