Definition
A period life table is a mortality table constructed from mortality rates observed across all ages within a single calendar year or short window, treating those rates as the mortality experience of a hypothetical cohort that lives entirely under that period's conditions.
Why it matters
Period life tables are the most common form of published mortality table because they require only one calendar period of observation. They produce the life expectancy figures that are most widely cited — "US female life expectancy at age 65 is approximately 21 years" — but those figures rest on the assumption that mortality conditions will not change over the cohort's remaining lifetime, which is generally not how a real cohort's life will unfold.
How it works
A period life table is built from observed deaths and exposures across the population at every age during a single calendar year, or a short window such as three calendar years averaged together. The age-specific mortality rates measured during that period are then applied sequentially to a hypothetical cohort, producing the survival probabilities, expected remaining life, and other derived figures the table contains. The interpretation is that of a synthetic cohort: a person aged 65 in the table year, if they could live their entire remaining life under that year's mortality conditions, would experience these probabilities. Because mortality conditions change over time — generally improving over the past century — the synthetic cohort is not the actual experience any real cohort will have. The figures are nonetheless useful: they describe current conditions accurately, they can be compared across calendar periods to measure improvement, and they are the input from which the period component of more complex tables (cohort, projected) is built. The CDC's National Center for Health Statistics publishes period life tables for the US population annually, and the Social Security Administration publishes its own period tables on a similar schedule.
In practice
Period-life-table figures are what most published "life expectancy at 65" numbers actually are. For an individual planning around their own longevity, the period figure understates the lifespan they should plan for, because it does not incorporate the mortality improvement they are likely to experience over their remaining life. A professional building lifetime income projections should generally be using a projected mortality table, not a period table, for any forward-looking calculation — though period tables remain the right tool for measuring current mortality conditions and for cross-period comparisons. Asking whether an income illustration uses a period or projected table is a reasonable question, and the answer reveals what assumptions are embedded in the forward-looking figures.
In the Longevity Standard Framework
A period life table is supporting vocabulary in the Longevity Standard framework as one of the reference structures the actuarial model can be configured against. The focal individual configuration uses a Gompertz mortality assumption with SOA credibility scaling rather than a period life table directly. The choice between a period table and a projected table for any specific finding shifts the framework's numerical outputs and is documented as part of every claim's parameter set; cross-arrangement comparisons within the framework hold the mortality basis constant so that differences in cost of income and realized value reflect arrangement structure rather than mortality choice.
Related terms
- Cohort life table
- Mortality table
- Projected mortality table
- Mortality improvement
- Survival curve
- Life expectancy
- Mortality rate
- SOA mortality research