Body weight (BMI) & life expectancy
A BMI in the healthy range is linked to the lowest mortality; both obesity and being underweight raise risk.
Why it matters (the mechanism)
Excess body fat drives insulin resistance, hypertension and inflammation; being underweight can signal frailty or underlying illness.
The evidence
Lowest mortality is seen around BMI 21–25 (WHO). Class II–III obesity is associated with roughly 3+ years of reduced life expectancy, mediated largely through diabetes and heart disease.
What to do
- Aim for a BMI roughly in the 21–25 range (use waist circumference too — it captures risk BMI misses).
- Weight follows diet and activity; change those rather than chasing the scale alone.
- Modest, sustained loss (5–10% of body weight) already improves blood pressure and blood sugar.
- If underweight, check for an underlying cause with a clinician.
And the chance of reaching 100?
Your odds of reaching 100 rise steeply with your overall forecast. As an illustration, a forecast age of 85 implies roughly a 6.7% chance of reaching 100; a forecast of 92 implies around 21%. Factors like body weight (bmi) shift where your forecast lands. Get your personal figure in the calculator.
These figures are population-average estimates from peer-reviewed research, applied on top of the official life-table baseline for your country, sex and birth cohort — the US Social Security Administration period life tables, the UK Office for National Statistics, and the WHO Global Health Observatory. They describe statistical tendencies, not personal certainties, and are not medical advice.
Other factors
Frequently Asked Questions
See how body weight (bmi) and everything else combine in your forecast — plus your chance of reaching 100.
Life Expectancy Calculator →