It's an actuarial calculation with good statistics on (for governments and large corporations) very large populations. So the estimates are accurate. But mostly, defined benefit pensions do not go the the heirs, so there is more money for the people getting the pension.
> But mostly, defined benefit pensions do not go the the heirs,
Right, most DB pensions I've seen, public or private, extend benefits at full value to exactly one designated person after the covered worker dies, for life, and then expire.
I have not seen that in the US. Usually, you get to choose how much benefit you want to go to a spouse, inversely correlated with the benefit you receive.
So you can choose your whole monthly benefit for just your life, then less for a joint and survivor (J&S) 50% benefit, and an even lesser amount for J&S 75% benefit, and finally a J&S 100% benefit option.
My grandmother had a pension which came from her late husband (in addition to her own pension). She avoided remarrying because that would have also terminated that survivor pension, apparently. She cohabited for decades with a man (my de-facto grandfather) who also collected a similar pension from his late wife. A rather silly restriction, if you ask me. They made the right call.
