Plain-English definitions of the terms used across the calculator and blog — no medical degree required.
The statistical average number of years a person is expected to live, calculated from current mortality rates at every age. It's a population-level estimate, not a prediction for any one individual.
A ratio of weight to height squared, used as a rough population-level health screening tool. It can't distinguish muscle from fat and doesn't account for where fat is stored. See our full breakdown on BMI's limitations.
Period life expectancy applies today's death rates to a hypothetical newborn as if they'll never change. Cohort life expectancy tracks what actually happens to real people born in a given year over their whole lives — and is almost always higher, since it captures future medical progress. Most headline "life expectancy" numbers you see are period estimates.
A statistical table showing the probability of death at every age for a population, used by demographers, insurers, and public health agencies to calculate life expectancy.
Diseases affecting the heart and blood vessels — including heart disease and stroke. It's consistently the leading cause of death in the United States.
Extended periods of low physical activity, such as prolonged sitting. Research links it to elevated mortality risk independent of whether someone also exercises regularly.
When a statistical association actually runs backward from how it's usually framed — for example, "long sleep is linked to poor health" may partly reflect that sick people sleep more, not that sleeping long makes you sick.
A flaw in older alcohol research where "non-drinkers" included former heavy drinkers who quit due to health problems, making abstainers look artificially unhealthy and moderate drinking look artificially protective.
The original name for what's now called BMI, developed in the 1830s by Belgian mathematician Adolphe Quetelet — not as a health tool, but to describe population averages.
The CDC's formal term for what's commonly called an "accident" — a leading cause of death, especially for younger age groups.