And it's even more complicated under the covers. My understanding is what they do is that they project the cash flows for each possible claiming strategy... So claiming each month between 62 if you're currently under 62 and age 70. Of course if you have a married couple and two people, there many more possible claiming strategies. Then they multiply those cash outflows by the probability of one or the other of you being alive to receive them. And then they discount the adjusted cash outflows for the time value of money. And they do that for many many possible sequences and see which one comes out the winner.