Taxing the B-A gains when they are sold, even after death, is what people mean by "eliminating the stepped-up basis" as the original poster suggested doing. At

Taxing the B-A gains when they are sold, even after death, is what people mean by "eliminating the stepped-up basis" as the original poster suggested doing. At present, when a heir inherits at B they pay estate tax at B, but then if they sell at price C they only pay tax on (C-B). As for knowing what A is, if you don't know it you can always fill in 0 and pay slightly more tax than you should, to be safe, so you don't caught in an audit. As of 2011 the IRS requires all brokers to track and report the cost basis for all purchases- that is, any purchase made after 2011 when you sell it they will tell you and the government what the value of A should be.