Five models you can push on

Human mortality after about age 30 is close to an exponential: the annual risk of dying doubles every eight years or so. Add a flat term for the deaths that have nothing to do with ageing — accidents, infections, violence — and you have the Gompertz–Makeham hazard. This tool integrates that hazard numerically and reports life expectancy at birth, 40, 60 and 80, median survival, and the odds of reaching 100. The reason to build it is one specific asymmetry: removing every extrinsic death is worth about two years, and adding two years to the doubling time is worth decades.

Longevity escape velocity is an accounting identity before it is anything else. Each calendar year costs you roughly one year of remaining life expectancy and returns whatever rejuvenation research delivers that year. Above one year gained per year, remaining life expectancy rises and does not come back down. Below it, you die later than you would have, and you still die. Set the age, the arrival year, the annual gain and its drift, and the model runs the trajectory to a death year or an escape year. It exists to show how much rides on a single number that has never been demonstrated.