Method
How Life Expectancy Is Calculated
Life expectancy is not guessed from one person's story. It is calculated from mortality rates across a population, organized into a life table.
The basic idea
A life table starts with a hypothetical group of people and applies observed death rates at each age. As the group moves through each age, some people statistically die and others continue into the next year.
From that structure, actuaries can estimate the average number of years remaining for someone who has already reached a specific age. That is why life expectancy at birth is different from life expectancy at age 70.
Why reaching an age changes the answer
Once someone has reached 50, 60, or 70, they have already passed earlier-life risks. The remaining-life estimate is based on people who made it to that exact age, not on newborns.
That is also why a person age 80 can still have several statistical years remaining in a life table. The table is conditional on already being 80.
What the calculator adds
The calculator looks up the age and sex row, interpolates between whole ages when a birth date is used, and converts the remaining years into weeks, days, months, seasons, birthdays, and biweekly paychecks.
Those translations do not add new predictive power. They are simply different ways to understand the same population average.
Questions
Is life expectancy an average?
Yes. It is an average across a population table, not a most likely age for a specific person.
Can the number change over time?
Yes. New mortality data, public health changes, and updated government tables can change future estimates.