The billionaire minimum tax, as it is commonly known, would increase the complexity of the tax code by using a non-traditional and difficult-to-measure definition of income. It would require formulaic rules for valuing different types of assets, payment periods that vary by asset type, and a separate tax system to deal with illiquid assets. This tax design goes well beyond international norms, where capital gains are taxed when realized and at lower rates than the US in many cases.