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Is there an online cost-basis calculator that automatically accounts for dividend re-investments and splits? 
Reinvestment creates a nightmare when it comes time to do taxes, sadly. Tons of annoying little transactions that happened automatically... Here's one article trying to answer your question: http://www.smartmoney.com/personal-finance/taxes/figuring-out-your-cost-basis-when-youve-lost-the-statements-9529/ You could also try this thing: http://www.gainskeeper.com/us/BasisProIndividual.aspx But I couldn't tell you if it would help. If it makes you feel better, brokerages are now required by the IRS to track your basis for you, so for new transactions and assets you shouldn't end up in this situation. Doesn't help with the old stuff ;-)