Do My NumbersMethodology

How the life expectancy calculator works

The life expectancy calculator reads one row of the SSA life table per future year and builds everything else from it: the chance of reaching each age, the average years left, and for a couple the chance that at least one of you gets there.

From yearly death rates to an expected age

qx=table value at age xq_{x} = \text{table value at age } x
Death probability qₓ: The chance that someone aged exactly x dies before reaching x + 1, read from the life table.
qx′=min⁡(1,  m qx)q'_{x} = \min\left(1,\; m\,q_{x}\right)
Adjusted death probability: The one-year death probability after the smoker adjustment: the table rate times the multiplier m, capped at 1.
kpx=∏j=0k−1(1−qx+j){}_{k}p_{x} = \prod_{j=0}^{k-1} \left(1 - q_{x+j}\right)
Survival probability ₖpₓ: The chance that someone aged x is still alive k whole years from now. It multiplies (1 − q) for each year in turn.
e˚x=∑k≥0kpx(1−12 qx+k)\mathring{e}_{x} = \sum_{k \ge 0} {}_{k}p_{x} \left(1 - \tfrac{1}{2}\,q_{x+k}\right)
Complete life expectancy e̊ₓ: The average number of years still to live for someone aged x, counting part years. The ring marks the complete version.
PA=1−(1−A−xpx)(1−A−ypy)P_{A} = 1 - \left(1 - {}_{A-x}p_{x}\right)\left(1 - {}_{A-y}p_{y}\right)
Chance at least one reaches A: The chance that at least one of two people lives to age A, each reaching A in their own time. It assumes their lifetimes are independent.

The expectancy formula credits half a year to anyone who dies during a year, which is what spreading deaths evenly through the year implies. With that assumption the calculator reproduces the SSA’s printed life expectancy at every age from 40 up, to within 0.01 years, which is what its tests check. The median and quartile ages on the page are the ages where the survival chance first falls to one half and one quarter.

For a couple, the two lifetimes are treated as independent, so the chance that at least one of you reaches an age is one minus the chance that neither does.

Starting values

  • A 65-year-old man who doesn’t smoke. A usual age to retire, and one where anyone can check the result against the SSA’s printed figure.
  • Smoker multiplier 2.0. Applied to every yearly death rate when “smoker” is ticked, and adjustable under Advanced. It is a rough scaling of a population table, not a table built from smokers.
  • Spouse 63, off until switched on. An illustrative two-year gap; the couple view only appears when asked for.

The table it reads

  • SSA period life table (2023), Social Security Administration, Office of the Chief Actuary. Edition: Period Life Table, 2023, as used in the 2026 Trustees Report. Retrieved October 22, 2026.

Each file keeps its source address, edition and retrieval date, and is tested against figures the publisher prints. All of them are listed on the data sources page.

What the numbers can’t tell you

  • How long any one person will live. The figures are averages over the whole Social Security area population, healthy and ill alike.
  • The effect of falling death rates after 2023. A cohort table would project those; this calculator does not.
  • Health, income, education, weight or where you live, none of which is an input.
  • How couples’ lifetimes are linked by shared homes and habits.