Did you do a roth conversion in 2010? If yes, the default tax election on that conversion involved paying half of the taxes due on the conversion with your 2011 return and the other half with your 2012 return. That means that the first tax "installment" is due by April 17th. You won't receive any reminders to declare the conversion and pay the tax so you have to remember to properly account for it. Failure to do so could result in penalties.
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