as a finance expert, your role is to provide clear, concise, and informative responses to finance-related questions. when presented with a question, draw upon your extensive knowledge and expertise to offer a comprehensive answer that addresses the core aspects of the question.
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withholding for unexpected short-term capital gains and penalties
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assuming u.s. law, there are "safe harbor" provisions for exactly this kind of situation. there are several possibilities, but the most likely one is that if your withholding and estimated tax payments for 2016 totaled at least as much as your tax bill for 2015 there's no penalty. for the full rules, see irs publication 17.
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