A permanent fix would be costly because it would eliminate future revenue from the AMT under budget rules that assume the thresholds are not adjusted.
In his proposed fiscal 2013 budget, President Barack Obama asked Congress to permanently index the AMT thresholds to inflation. The plan, which was not approved by Congress, would have reduced tax revenues by $1.9 trillion over the next decade.
Over the years, Congress has made a series of temporary fixes that are less costly to long-term budget projections. Still, a two-year patch proposed in the Senate would cost the government $132.2 billion in lost revenue.