Starting age changes the meaning
“Life expectancy at birth” and “life expectancy at age 40” are not two labels for the same statistic. At birth, the calculation includes mortality risk from infancy onward. At age 40, the calculation concerns people who have already reached 40. It summarizes expected remaining years from that point, or—as in the Chetty study—reports the corresponding expected age at death.
This distinction matters because surviving to 40 supplies information that was not available at birth. An age-40 estimate cannot simply be substituted for a birth estimate without changing the population and conditioning behind the number.
What the Chetty baseline contributes
Chetty and colleagues estimated race- and ethnicity-adjusted life expectancy at age 40 by household income percentile and sex. Life Days Left selects the 75th household-income percentile and takes the arithmetic mean of the published male and female expected ages at death. The resulting baseline is 85.0786285 years.
That is an explicit editorial choice. It is not the U.S. average, not a claim about any visitor’s income, and not an estimate recalculated from information about the viewer. The income and life expectancy explainer describes what this source can and cannot support.
What the SSA input contributes
The SSA 2026 table supplies cohort life expectancy at birth by sex and calendar year under the Intermediate assumptions. The model averages the male and female entries for each birth year. It then subtracts the same unisex value for 1967, the midpoint year associated with the age-40 Chetty sample period.
Chetty p75 unisex baseline + [SSA cohort e0(birth year) − SSA cohort e0(1967)]For a 1967 birth year, the bracketed term is zero. For another birth year, the term moves the baseline only by the difference in the SSA cohort series. The model does not add two life expectancies together, and it does not call the SSA at-birth value a personalized age at death.
Why this is a hybrid estimate
The construction borrows an income-linked level from one study and a cohort trend from another source. That gives the chart a deterministic rule for making birth-year comparisons, but it does not reproduce either source’s full model. The source populations, periods, and starting ages differ.
Once the estimated age is set, the site multiplies it by 365.2425 days and subtracts exact calendar days lived from the supplied birth date. The displayed percentage divides those remaining days by the modeled lifetime and rounds to a whole percent. See every step on the methodology page.