How Is Your Life Expectancy Calculated?

1. WHO baseline by country and gender

The starting point is WHO life expectancy data for your country and gender. The specific number we use is called period life expectancy at birth. It answers a precise question: if a baby were born today and lived their whole life under the mortality rates currently observed in your country, how many years on average would they live? It is built by taking the chance of dying in each one-year age band right now and stitching those probabilities together into a single average lifespan.

Period life expectancy has two important limitations. First, it freezes today's mortality rates and projects them forward, so it doesn't account for medical advances (or setbacks like pandemics) over the coming decades. Second, it is an average — the distribution of actual lifespans around that average is wide, with one tail in the seventies and another stretching past one hundred. We use period life expectancy because it is the standard, transparent figure published consistently across more than 190 countries, but it is the baseline, not the verdict.

2. Age-conditional adjustment

Life expectancy at birth systematically underestimates remaining years for people who have already survived past childhood. The reason is that the at-birth average is dragged down by everyone who dies young — infants, accident victims in their twenties, early cancers. If you're 70, you already cleared those hurdles, and your statistically expected remaining lifespan is longer than a naive "average minus age" calculation would suggest.

Demographers handle this with a tool called a life table. A life table tracks a hypothetical group of 100,000 newborns, applies the current mortality rate at each age, and records how many are still alive at age 1, age 2, and so on. From that you can read off a quantity written e(x) — the expected remaining years for someone who has reached age x. For a US male, e(0) is about 75, but e(70) is roughly 13 — meaning a 70-year-old American man's statistical expected end is around 83, not 75.

Your Death Timer approximates this by starting from a reference US-male life-table curve for e(x), then scaling it by the ratio of your country and gender baseline to that reference (74.8 years). This gives a continuous estimate of remaining years at any age that respects the conditional-survival effect without requiring us to ship full life tables for every country in the world. It is an approximation, but it tracks the published age-specific life expectancies of high-income countries closely.

3. Lifestyle adjustments

If you answer the optional lifestyle questions, we add or subtract years from the conditional baseline. Each adjustment is anchored to a specific, published effect size:

• Smoking. The CDC and Doll & Peto's long-running British Doctors Study both put the cost of heavy smoking at 8–10 years; light smoking at roughly 4 years. Quitting before 40 recovers about 90% of the excess risk, so ex-smokers are penalised much less than current smokers.
• Body mass index. The Prospective Studies Collaboration meta-analysis of nearly a million adults found a U-shaped curve: a BMI of 22–25 is the sweet spot, with each 5-unit increase above that costing 2–4 years on average, and severe underweight also raising mortality.
• Exercise. A Harvard analysis of more than 650,000 adults found that meeting the 150-minute-per-week moderate exercise guideline is associated with 3–5 extra years. The dose-response curve plateaus around 300–450 minutes per week.
• Alcohol. Heavy daily drinking (4+ drinks per day) costs 4–5 years on average; moderate drinking is roughly neutral, with some studies showing a small benefit and others showing none after correcting for sick-quitter bias.
• Diet. The PREDIMED trial and other Mediterranean-diet studies show roughly 2–3 added years for diets rich in vegetables, legumes, whole grains and olive oil compared to a high-processed-food baseline.

On the results page the breakdown of each adjustment is shown explicitly, so you can see how the final number was built and disagree with any individual component.

4. Conversion to days, hours, minutes, seconds

Once the adjusted remaining years are known, we add them to the current moment to produce an expected end date, using 365.25 days per year to account for leap years. The countdown then ticks in real time from your device clock. The seconds digit visibly moves not because we claim that level of precision — we obviously don't — but because the steady tick is the point: it makes the abstract number behave like time, which is what makes a memento mori tool actually land.

5. What the timer is — and what it isn't

The timer is a statistical average for someone who shares your country, gender, age and (optionally) broad lifestyle profile. It is the kind of number an actuary would use to price a life-insurance product across a population of millions, repackaged into something that's emotionally legible to one person.

It is not a medical forecast, a diagnosis, or a substitute for talking to a physician. It cannot see your genome, your blood work, your family history, accidents you haven't had yet, or the trajectory of medicine over the coming decades. Real individual lifespans are distributed widely around any average. Use the countdown as a prompt for reflection and prioritisation — not as a prediction.