A. Interests from tax-free bonds issued to finance privately owned projects, such as assisted living residences and sports stadiums, may be subject to AMT. Although some closed-end municipal funds are named AMT-free and avoid such debt, others maybe subject to AMT.
Those subject to AMT tend to yield more than most tax-exempts because AMT-eligible projects are often unrated and riskier than everyday school, highway, and general obligation bonds.
Unfortunately there is no dollar threshold for the AMT - if your income is low, you generally don't have to worry about it, and it's possible for high income families and still owe no AMT. It all depends on the amount of income and its sources, as well as the types and sizes of deductions you claim (some deductions allowed under the regular income tax rules are forbidden under AMT).