Twin, I think you might have found a glitch in the formula, it’s from a book I read once. In your case it would have to be what the investment was when it was given to you. Everything accumulated after that is considered your own because it was you who, instead of spending it, left it in stocks and bonds. That difference would not be inherited. It would be your earning that you gained by simply saving.

BTW: I edited the orignal post to explain it a bit more.