How life expectancy is calculated (and why online calculators disagree)
Short answer: a life expectancy calculator starts from a life table — the average age at death for people of your country and sex — adjusts it for the age you have already reached, then adds or subtracts years for habits such as smoking and exercise. Calculators disagree because each one uses a different table, a different age adjustment and different sizes for each habit.
Step 1: a life table
National statistics offices and the WHO publish life tables: for each age, the share of people who die before the next birthday. From that table you get life expectancy at birth. Worldwide it is a little over 70 years in recent WHO data, and it differs by country and by sex — women live several years longer on average.
Step 2: adjust for your current age
Life expectancy at birth includes everyone who dies young. If you are already 50, you have survived those years, so your expected age at death is higher than the at-birth number. This is called remaining life expectancy. Calculators that skip this step are the ones that tell a 70-year-old they have a few years left — or that they "died 20 years ago".
Step 3: lifestyle adjustments
Large long-term studies compare groups of people with different habits. A calculator turns those comparisons into plus or minus years: smoking, heavy drinking, activity, sleep, diet, weight, sitting time and conditions such as diabetes or high blood pressure.
Why two calculators give different numbers
- Different baselines. One uses a world average, another a national table, another an old table.
- No age adjustment. Without step 2, older users get numbers that are too low.
- Different habit sizes. One gives exercise +1 year, another +7. Some double-count habits that overlap, such as weight and activity.
- Hidden math. If the result is just one number, you cannot tell which answer moved it.
- Too few or vague questions. "Do you exercise?" means little without how many minutes a week.
How to read any result
Treat it as a direction, not a date. The useful part is the gap between your current habits and your best realistic habits — and which habit makes the biggest part of that gap.
How Spanlet calculates
Spanlet starts from average life expectancy for your country and sex, adjusts it for your current age, then adds or subtracts conservative, capped amounts for each habit and shows every one in years. The result never drops below your current age plus one year, and you can change any answer to see the effect instantly.
These numbers are population averages from published research, not a prediction for you. They are not medical advice — talk to a doctor about your health.
FAQ
What is the difference between life expectancy and remaining life expectancy?
Life expectancy at birth is the average age at death for a newborn. Remaining life expectancy is the average number of years left for someone who has already reached a given age, so the expected age at death rises as you get older.
Why does one calculator say 75 and another say 88?
They start from different baseline tables, some ignore your current age, and they give each habit a different weight. A calculator that shows each adjustment in years lets you see where the difference comes from.
Can a calculator tell me when I will die?
No. It gives an average for people with answers like yours. Real lifespans vary widely around that average.