Speaking as a professional tax preparer, if you make more than $40k, have dependents and live in a high-tax state, you can be touched by AMT. Obviously, the more you are over $40k, the more you are endangered.
If you want to avoid penalties and interest for under-withholding, use your AGI (bottom of 1040), add back non-repeating adjustments, compute tax based upon your filing status from the tables and subtract your normal withholding from wages.
If that figure is close to zero, why give any more interest-free loan than you have to. If your withholding equals your 2011 tax burden [not refund or balance due, you fool], forget it for 2012 at least because you are ‘safe harbor’ed.
Otherwise divide by the 4 quarterly payments and feed the pig. AMT is a B*$%H and an obscenity to logic especially since it became a game for the politicians.
Wouldn’t you do better just to make sure you pay at least 100% of what you owed in 2011, or 110% if your AGI is over $175K?