Mortality doubling time

Mortality doubling time (MDT) is the number of years it takes for age-specific mortality risk to double, derived directly from the Gompertz exponent b as MDT = ln(2)/b. In contemporary high-income populations, the MDT for all-cause mortality is approximately 7–8 years in mid-adulthood, meaning a 50-year-old's annual risk of dying is roughly twice that of a 42–43-year-old. MDT is a compact summary of the rate of actuarial ageing and is used comparatively across species (where it varies from months in short-lived organisms to ~8 years in humans, while species such as the naked mole-rat appear to defy Gompertz dynamics entirely with no detectable increase in hazard rate over decades of life — Ruby et al., eLife 2018) and across population subgroups, enabling detection of interventions that alter ageing rate rather than merely shifting baseline mortality.