The simplest way to establish taxes at the business unit level is to charge
them a flat tax at the marginal rate of taxation on their income. This
marginal rate should include the top tax rates likely to be imposed on
taxable income at the federal, state, and local levels.
This method will drive desirable behavior
in that decisions at the margin are likely to have marginal tax rate
consequences. Thus, this rate will encourage the most economical
trade-offs for most projects.
The drawback of this method is that it does
not account for exclusions to taxable income or temporary differences
that would result in lower actual taxes. For example, if the business
unit generated foreign tax credits, they would not be recognized in a
flat rate regime even though the corporation and its shareholders would
benefit. Also, if the business unit were able to defer taxes, those
would be reflected neither as reductions to capital nor as cash benefits
in the current period. Since no company actually pays taxes on total
income equal to the marginal statutory rates, a business unit using this
method would invariably report a lower EVA than it is contributing to
the company.