The model
The starting point is the risk of dying in the coming year for an average American of your age and sex. We use a Gompertz–Makeham curve fitted to current US period life tables. It captures the most reliable pattern in human mortality: after early adulthood, yearly risk roughly doubles every eight years.
Each measure you enter adjusts that risk using a hazard ratio (HR) from a large prospective study or meta-analysis. An HR of 1.5 means 50% higher yearly risk; an HR of 0.8 means 20% lower.
Hazard ratios are applied on a log scale and interpolated smoothly between the categories the studies report, so a small change in a measurement never causes a sudden jump in your result.
Biological age
Your biological age is the age at which an average person of your sex has the same yearly risk you do. Because risk doubles about every 8.2 years (a Gompertz slope of 0.085 per year):
biological age = age + ln(combined HR) ÷ 0.085
A combined HR of 2 adds about 8 years. A combined HR of 0.5 subtracts about 8.
Life expectancy and the range
We multiply your age-specific risk by your combined HR at every future age and follow the resulting survival curve to age 120. Your life expectancy is the average age reached on that curve. The middle 50% range runs from the age by which a quarter of people with your profile would have died to the age by which three quarters would have. That range is wide by nature, and it’s the most honest way to show what any individual estimate can tell you.
The model assumes your measures stay where they are today. Improving them changes the curve, which is the point of retesting.
How overlapping measures are combined
Some measures reflect the same thing. BMI and waist size both track body fat; resting pulse and VO₂max both track fitness; the four physical tests all track strength and mobility. Adding their hazard ratios at full weight would count the same risk twice.
So measures are grouped: physical function, body size, cardiorespiratory fitness, blood pressure, and each habit on its own. Within a group, the measure with the strongest signal counts in full and the others count at 40%. The combined total across groups is then reduced by 15%, because even different groups are partly correlated (people who exercise more also tend to sleep better and weigh less). The combined HR is capped between 0.3 and 8.
Measures you leave blank count as typical. They neither help nor hurt.
Physical function
Sitting-rising test
In about 2,000 adults aged 51 to 80 followed for six years, those scoring 0 to 3 had about 5 times the mortality of those scoring 8 to 10, after adjusting for age, sex and BMI. The test combines leg strength, flexibility, balance and body composition in a single movement. We interpolate between the study’s four score bands and compare you with a typical score for your age, which falls from about 9 in your thirties to about 4.5 in your seventies.
10-second one-leg stand
Among about 1,700 adults aged 51 to 75, those unable to hold a one-leg stand for 10 seconds had an 84% higher adjusted risk of death over seven years. The share who can’t do it rises steeply with age, from about 5% in the early fifties to about half by the mid seventies, so a pass counts for more as you get older.
Five chair stands
Across pooled cohorts, the slowest chair-rise times carried about twice the mortality of the fastest. We use the standard Short Physical Performance Battery time bands (under 11.2 s, 11.2–13.7, 13.7–16.7, and over 16.7 s), plus a separate value for being unable to complete the stands without using your arms.
Usual walking speed
In a pooled analysis of nine cohorts and over 34,000 older adults, each 0.1 m/s faster usual walking speed was linked to 12% lower mortality. Speed is measured against a typical pace for your age (about 1.3 m/s under 60, falling to about 0.95 m/s over 80). Any benefit is capped at 0.3 m/s above typical, because the original data come from older adults.
Body and vitals
Body mass index
Among 10.6 million participants in 239 studies, never-smokers without chronic disease had the lowest mortality at a BMI of about 20 to 25. Risk rose to about 1.45 at a BMI of 30 to 35 and 2.76 at 40 or more, and also rose at a BMI below 18.5. BMI shares a group with waist-to-height ratio.
Waist-to-height ratio
Waist size relative to height tracks visceral fat, the metabolically active fat around the organs, better than weight does. The NICE guideline recommends keeping your waist under half your height. Risk climbs steadily above a ratio of 0.5 and steeply above 0.6.
Resting heart rate
Meta-analyses of over a million participants find all-cause mortality rises about 9% to 17% for every 10 beats per minute. We use the midpoint, with no extra credit below 60 bpm, since very low rates mostly reflect fitness, which VO₂max already captures. Resting pulse shares a group with VO₂max.
Blood pressure
Across 61 studies and a million adults, vascular death roughly doubled for each 20 mmHg higher systolic pressure above 115. All-cause mortality rises less steeply, so we use a more conservative curve: about 1.15 at 135, 1.35 at 150 and 2.0 at 190 mmHg. Systolic pressure drives the estimate; diastolic is recorded for your summary.
Cardiorespiratory fitness
VO₂max
In a meta-analysis of 33 studies, each extra MET of fitness (3.5 ml/kg/min of VO₂max) lowered all-cause mortality by 13%. Your VO₂max is compared with the median for your age and sex in the FRIEND registry of treadmill tests, and the difference is capped at ±4 METs. You can estimate VO₂max three ways, from least to most accurate:
- Resting heart rate (Uth et al. 2004): VO₂max ≈ 15.3 × (208 − 0.7 × age) ÷ resting HR. Rough, about ±15%.
- Queens College step test (McArdle et al. 1972): men 111.33 − 0.42 × HR; women 65.81 − 0.1847 × HR, where HR is your recovery pulse per minute.
- A smartwatch or lab reading, entered directly.
Daily habits
Tobacco
Current smokers had about three times the mortality of never-smokers, losing at least a decade of life. Quitting before 40 recovered about 90% of that loss. Former smokers are scored by how long ago they quit.
Exercise
In 661,000 adults, meeting the 150-minute weekly guideline lowered mortality by about 31% compared with no activity, and the benefit kept growing until about three times the guideline, then leveled off. No harm was seen at higher amounts.
Sleep
A meta-analysis of 1.3 million people found 12% higher mortality with habitually short sleep and 30% higher with long sleep. Long sleep may partly reflect existing illness rather than cause it, so we apply that end of the curve cautiously.
Alcohol
In 600,000 current drinkers, mortality rose above about 100 g of alcohol a week, which is roughly seven US standard drinks. We give no credit for light drinking, since apparent benefits in older studies are largely explained by former drinkers being counted as non-drinkers.
Fruits and vegetables
Across two million people, about five servings a day (two fruit, three vegetables) was linked to 13% lower mortality than two a day, with no added benefit beyond five.
Social connection
Across 70 studies, loneliness and social isolation each raised mortality by about 26% to 29%, a risk comparable to obesity.
Limitations
- It ignores diagnosed disease. Heart disease, cancer, diabetes, kidney disease and many other conditions change life expectancy far more than anything here. If you have one, your clinician’s view matters more than this estimate.
- Associations aren’t causes. A slow chair-stand time is a marker of risk; improving it likely helps, but the studies don’t prove by how much.
- The studies vary. Several physical tests were studied in people over 50. Applied to younger adults, the results are extrapolations.
- Combining is approximate. No single study measured all fifteen together. The grouping and shrinkage rules are our reasoned estimate of how much these measures overlap.
- Home measurement is noisy. Tape position, cuff size, and a stopwatch thumb all add error. Repeat tests and use your typical result.
- US baseline. The life table is American. Elsewhere, baseline life expectancy may be several years higher or lower.