For nearly 100 years, states have based their taxes on federal taxes, most notably those addressing estate tax and depreciation. But when the federal government decides to reduce—or eradicate—certain taxes, states face significant losses in revenue. To recoup their losses, some states vote to "decouple" themselves from certain federal taxes and write their own tax codes.
Of course, that just makes filing taxes more complicated for you.
After President Bush's bill to repeal the estate tax passed Congress, 18 states passed legislation to decouple their estate tax laws from the federal tax law. (The 18 states are highlighted in the map.) In addition, the federal government's push to change how businesses depreciate equipment, for example, is not widely accepted by state tax bodies. (The biggest hurdle for states to overcome is what is known as "bonus" depreciation, which allows businesses to write off up to 50 percent of an asset during the first year rather than depreciating the full amount during the useful life of the asset.)