Concept Architecture
Concept
Theoretically, Life Expectancy is a demographic and epidemiological measure representing the average number of years an individual is expected to live, assuming that current age-specific mortality rates remain constant throughout their lifetime. It is one of the most fundamental summary measures of population health and is grounded in probability theory, actuarial science and life table methodology. The concept exists to summarise mortality experience into a single interpretable statistic for comparing populations, monitoring health trends and evaluating health interventions.
Mathematically, Life Expectancy is estimated from a life table by calculating the total remaining person-years lived beyond a specified age and dividing this value by the number of individuals surviving to that age. The calculation incorporates age-specific mortality probabilities and survival functions, providing an expected remaining lifetime conditional upon survival to a given age.
In practice, Life Expectancy is calculated using national mortality statistics, census data and demographic life tables. It is widely used by governments, international organisations and health economists to assess population health, monitor inequalities, evaluate healthcare systems and estimate long-term outcomes within economic evaluations and disease burden studies.
Purpose
Used to summarise population mortality, compare health outcomes across populations, evaluate healthcare performance, monitor health inequalities and support demographic, epidemiological and health economic analyses.
Mathematical Formulae
Primary Formula
Life Expectancy at Age x = Tx � lx
where:
- Tx = total person-years remaining beyond age x
- lx = number of survivors at age x
Supporting Formulae
Tx = �Ly
where Ly represents person-years lived in each remaining age interval.
Probability of Survival
S(x) = lx � l?
where l? is the initial life table population.
Related Mathematical Methods
- Life table analysis
- Kaplan-Meier estimation
- Survival analysis
- Hazard function estimation
- Actuarial life table methods
- Multi-state life table modelling
Example
A life table shows that 90,000 individuals survive to age 50 and have a combined total of 2,970,000 remaining person-years.
Life Expectancy at Age 50 = 2,970,000 � 90,000
= 33.0 years
An individual aged 50 is therefore expected to live an average of 33 additional years, assuming current mortality rates remain unchanged.
Excel Implementation
| Function | Example Formula | Health Economics Application |
|---|---|---|
| SUM | =SUM(C2:C102) | Calculate total remaining person-years (Tx). |
| Division | =SUM(C2:C102)/B2 | Calculate life expectancy from a life table. |
| SUMPRODUCT | =SUMPRODUCT(B2:B102,C2:C102) | Aggregate weighted life table calculations. |
| IF | =IF(D2<80,"Below Benchmark","Meets Benchmark") | Compare life expectancy with policy targets. |
| AVERAGE | =AVERAGE(D2:D21) | Calculate average life expectancy across regions or populations. |
VBA (Optional)
Automate life table construction, life expectancy estimation by age and sex, and generation of demographic and health economic population reports.
Sources
- Chiang CL. The Life Table and Its Applications.
- Preston SH, Heuveline P, Guillot M. Demography: Measuring and Modelling Population Processes.
- World Health Organization. World Health Statistics.
- United Nations. World Population Prospects: Methodology of Life Tables.
- Drummond MF, Sculpher MJ, Claxton K, Stoddart GL, Torrance GW. Methods for the Economic Evaluation of Health Care Programmes.
- Briggs A, Claxton K, Sculpher M. Decision Modelling for Health Economic Evaluation.
Related Concepts (2)
Library
Publications
1
Health at a Glance 2023: OECD Indicators — Organisation for Economic Co-operation and Development, 2023 Edition ed., 2023 (OECD Publishing)
OECD’s comprehensive biennial compendium of comparative indicators on population health and health-system performance across member and partner countries — health status, risk factors, access, quality, resources and spending — the standard cross-country benchmarking reference.
Frequently Asked Questions (6)
What is life expectancy?
The average number of years an individual of a given age is expected to live, based on current age-specific mortality rates.
Source: Chiang 1984
What average lifespan does life expectancy express?
Life expectancy is the average number of years a person of a given age is expected to live. It expresses how much longer, on average, someone of that age will survive. It is based on current age-specific mortality rates, applying today's death rates at each age to project remaining years. It is measured from a given point, usually from birth but sometimes from a later age. It is the broader measure that healthy life expectancy refines, since life expectancy counts all years while healthy life expectancy counts only the healthy ones. Expected remaining years of life is what it expresses. Chiang (1984) set out the method.
Source: Chiang 1984
What does life expectancy express?
Life expectancy expresses the average number of years an individual of a given age is expected to live, so it gives the expected number of years of life from that age, based on current age-specific mortality rates. This expression of expected years defines it. So life expectancy is the average number of years an individual of a given age is expected to live, based on current age-specific mortality rates.
Source: Chiang 1984
What is life expectancy based on?
Life expectancy is based on current age-specific mortality rates, so the average years an individual of a given age is expected to live is calculated from the mortality rates that currently apply at each age. This basis in mortality rates defines it. So life expectancy is the average number of years an individual of a given age is expected to live, based on current age-specific mortality rates.
Source: Chiang 1984
From what point is life expectancy measured?
Life expectancy is measured from a given age, so it is the average number of years an individual of that age is expected to live, based on current age-specific mortality rates. This starting from a given age defines it. So life expectancy is the average number of years an individual of a given age is expected to live, based on current age-specific mortality rates This relationship is what makes healthy life expectancy the healthy portion of a person's total life expectancy.
Source: Chiang 1984
How does life expectancy relate to healthy life expectancy?
Life expectancy relates to healthy life expectancy as total years against years in good health: life expectancy is the average number of years an individual of a given age is expected to live, and healthy life expectancy is the average years expected to be lived in good health, adjusting for time in disability. So healthy life expectancy is the healthy portion of life expectancy, connected as total expected years and the years of them spent in good health.
Source: Chiang 1984
Trust Record
Verified by Dr Darrin Baines
British health economist
Professional identity: darrinbaines.org
Verification date: 11 Mar 2026
Content version: 1.0.0
Canonical Identity
- Persistent URI
- https://healtheconomics.wiki/concept/life-expectancy
- Term code
- HS-HP-PHO-012
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