Both of these calculators seem to to assume that revival technology is certain to be developed eventually, and it's just a matter of time before it is. (Moreover, they assume an exponential distribution for the time to develop it, which is naive, but not as pressing a problem.) The more concerning possibility is, I think, that a revival might not be possible at all.

Beyond that, I find it difficult to compute my own estimate this way because the risk of human negligence or dishonesty is by far my biggest concern (apart from the technological possibility of revival), and I don't have a good estimate of how likely this is. I could make something up, which seems to be popular, but then I could just make up the cryonics probability, too.