Definition
Lifespan versus life expectancy is the distinction between the actual length of an individual life (lifespan) and the statistical average of additional years a person of a given age is expected to live (life expectancy).
Why it matters
The two terms are routinely conflated, including by professionals, and the conflation has direct consequences for lifetime income planning because it treats a population average as if it were an individual forecast. Naming the distinction is what allows planning to take account of the lifespan distribution rather than collapsing it to a single number.
How it works
Lifespan is what one individual actually lives — a single realized number. Life expectancy is what the population of similar individuals lives on average — a statistical aggregate. The two are systematically conflated in popular discussion of retirement, where "life expectancy is 85" is taken to mean "you'll live to about 85." In fact, life expectancy is the mean (sometimes the median) of a wide distribution: for a US female at age 67, period life expectancy is roughly 19 years, but roughly a quarter live past age 95 and a smaller share past 100. Treating life expectancy as a personal prediction systematically underestimates the longevity tail and the planning horizon needed to cover it.
In practice
For an individual planning lifetime income, the lifespan-versus-life-expectancy distinction is what makes planning-horizon selection a strategic question rather than a mechanical lookup. Planning to one's life expectancy leaves roughly a 50% probability of outliving the plan, which is generally not the level of confidence the individual wants. A professional working with the individual should help select a planning horizon based on a target survival probability rather than on life expectancy directly — for example, planning to the age at which only 10% or 5% of the cohort remains alive. The distinction also explains why pooled and transferred-risk arrangements compete favorably with self-managed drawdown for longevity-averse individuals: the individual can hedge their own lifespan dispersion by pooling with others whose dispersion offsets theirs.
In the Longevity Standard Framework
The lifespan-versus-life-expectancy distinction is supporting vocabulary in the Longevity Standard framework. The framework's planning horizon is set explicitly to address the dispersion of lifespans around expectancy — the focal individual's planning age of 90 sits above the median lifespan (roughly age 86) but below the deeper tail. The cost of extra protection is the direct expression of the dispersion: it measures what the individual pays to plan further into the lifespan tail and is structurally why pooled arrangements deliver higher realized value at longer planning horizons.
Related terms
- Life expectancy
- Mortality rate
- Survival curve
- Maximum lifespan
- Healthy life expectancy
- Planning horizon risk
- Longevity tail risk
- Longevity risk