More Info (and maybe I figured it out?). My cost basis on the non-deductible IRA that had the withdrawal was $37,741. I was assuming that this basis only applied to the one account and not all accounts but maybe that's not the case, i.e. the non-taxable portion of the $100,000 withdrawal is a lot less when the total balance is bigger. So it looks like it spreads the cost basis across all accounts as opposed to the one that had the contributions. Make sense?
