How the calculator works
The calculator starts from a national baseline life expectancy figure, split by sex, drawn from the general pattern of U.S. actuarial life tables. It then applies estimated year adjustments for each lifestyle factor you enter, based on the general direction and rough magnitude found in published epidemiological research on that factor. These adjustments are added together to produce your result.
This is a simplified, illustrative model — not a clinical or actuarial risk assessment. Real medical underwriting incorporates actual health records and models how risk factors interact with each other, which a quick lifestyle calculator can't replicate. See our post on how accurate these tools really are for the full explanation.
General research areas referenced
- Smoking: long-running cohort studies including the British Doctors Study, plus U.S. Surgeon General reports on smoking and mortality.
- Alcohol: World Health Organization guidance on alcohol and health risk, and the "abstainer bias" issue identified in earlier moderate-drinking research.
- Exercise: population studies on physical activity and mortality risk, including research on diminishing returns at higher activity levels.
- Sleep: meta-analyses on sleep duration and mortality risk, showing the lowest risk in the 7-8 hour range.
- BMI: the history and limitations of Body Mass Index as a health screening tool, including its origin as the Quetelet Index.
- Social connection: the Harvard Study of Adult Development, one of the longest-running longitudinal studies of health and happiness.
For general reference on national statistics, the CDC's National Center for Health Statistics and the World Health Organization are good starting points if you want to dig into primary sources yourself.
Blog content
Each blog post cites the general category of research it's drawing from in the text itself. We paraphrase and summarize rather than quoting directly, and we try to flag genuine scientific uncertainty (like the sleep-duration reverse-causation issue) rather than overstating confidence.
Corrections
If you spot something that seems off or outdated, we'd genuinely like to know — get in touch.