Disability Adjusted Life Year (DALY): What It Means

Author: Ian C. Langtree - Writer/Editor for Disabled World (DW)
Published: 7 Nov 2011 - Updated: 5 Aug 2026
Publication Type: Informative

Table of Contents:
Synopsis - Definition - Overview - FAQs - Insights, Updates - Related Content

Synopsis

This information explains the Disability Adjusted Life Year, or DALY, a public health metric that expresses the overall burden of disease as the number of years lost to ill health, disability, or early death. First conceptualized by Murray and Lopez in the Global Burden of Disease study published in 1990 for the World Health Organization and the World Bank, the DALY combines two components into a single figure, adding Years of Life Lost to premature death and Years Lived with Disability so that mortality and morbidity are measured together. The concept matters to researchers, policymakers, clinicians, and disability advocates because it captures the weight of conditions that shorten healthy life without necessarily causing death, revealing, for instance, that psychiatric and neurologic conditions account for 28 percent of all years lived with disability yet only a small share of deaths. For people living with disabilities, seniors, and those tracking health equity, the measure offers a useful lens for understanding how chronic illness and impairment shape a population's true health picture beyond mortality figures alone.

At a Glance

• 1 - One DALY equals one lost year of healthy life.
• 2 - Japanese life expectancy statistics serve as the standard for measuring premature death because they are the longest in the world.
• 3 - Some studies apply social weighting that values years lived as a young adult more highly, peaking around age 25 and lowest for very young children and older people.
• 4 - The GBD 1990 and GBD 2004 studies discounted future years at a 3 percent rate, so a year of life saved next year is worth 97 percent of one saved this year.

Topic Definition

Disability Adjusted Life Year (DALY)

A Disability Adjusted Life Year, commonly shortened to DALY, is a summary measure of population health that quantifies the overall burden of a disease or injury as the total number of healthy years lost. It works by adding together two distinct components: the Years of Life Lost through premature death and the Years Lived with Disability caused by illness or impairment, collapsing both mortality and morbidity into one comparable figure. A single DALY represents one year of healthy life lost, and the sum of DALYs across a population reflects the gap between its current health status and an ideal in which everyone lives to old age free of disease and disability. Widely used by the World Health Organization in its Global Burden of Disease reporting, the DALY has become a standard reference point in public health planning and health impact assessment.

Overview

Disability-adjusted life year is a measure of overall disease burden, expressed as the number of years lost due to ill-health, disability or early death. Over the years various investigators have attempted to overcome these limitations by developing new metrics that factor in disability or quality of life along with mortality. One of the most recent, and still controversial, measures is the Disability-Adjusted Life Year, or DALY.

The DALY was first conceptualized by Murray and Lopez in work carried out with the World Health Organization (WHO) and the World Bank known as the global burden of disease study, which was published in 1990. It is now a key metric employed by the United Nations World Health Organization in such publications as its Global Burden of Disease.

Today the DALY is becoming an increasingly common term in the field of public health and health impact assessment. It extends the concept of potential years of life lost due to premature death to include equivalent years of healthy life lost by virtue of being in states of poor health or disability - mortality and morbidity are combined into a single, common metric.

Looking at the burden of disease via DALYs can reveal surprising things about a population's health. For example, the 1990 WHO report indicated that 5 of the 10 leading causes of disability were psychiatric conditions. Psychiatric and neurologic conditions account for 28% of all years lived with disability, but only 1.4% of all deaths and 1.1% of years of life lost. Thus, psychiatric disorders, while traditionally not regarded as a major epidemiological problem, are shown by consideration of disability years to have a huge impact on populations.

Disability Adjusted Life Year Formula

One DALY can be thought of as one lost year of "healthy" life. The sum of these DALYs across the population, or the burden of disease, can be thought of as a measurement of the gap between current health status and an ideal health situation where the entire population lives to an advanced age, free of disease and disability.

Traditionally, health liabilities were expressed using one measure: (expected or average number of) Years of Life Lost (YLL). Japanese life expectancy statistics are used as the standard for measuring premature death, as the Japanese have the longest life expectancies.

This measure does not take the impact of disability into account, which can be expressed by: Years Lived with Disability (YLD). DALYs are calculated by taking the sum of these two components.

DALY = YLL + YLD

The DALY relies on acceptance that the most appropriate measure of the effects of chronic illness is time, both time lost due to premature death and time spent disabled by disease. One DALY, therefore, is equal to one year of healthy life lost.

Some studies use DALYs calculated to place greater value on a year lived as a young adult. This formula produces average values around age 10 and age 55, a peak around age 25, and lowest values among very young children and very old people.

A crucial distinction among DALY studies is the use of "social weighting", in which the value of each year of life depends on age. Commonly, years lived as a young adult are valued more highly than years spent as a young child or older adult. This weighting system reflects society's interest in productivity and receiving a return on its investment in educating children. Society has invested relatively little in very young children, and it has already received a substantial return on its investment in older people. Young adults, however, have received the maximum amount of investment and, at the beginning of their working life, have had the least opportunity for society to benefit from its investment.

The global burden of disease (GBD) 2001-2002 study counted life years equally, but the GBD 1990 and GBD 2004 studies used the following formula:

W = 0.1658 Y e-0.04 Y

Where Y is the age at which the year is lived and W is the value assigned to it relative to an average value of 1.

In these studies future years were also discounted at a 3% rate, so that a weighted year of life saved next year is worth 97% of a year of life saved this year.

The effects of the interplay between life expectancy and years lost, discounting, and social weighting are complex, depending on the severity and duration of illness. For example, the parameters used in the GBD 1990 study generally give greater weight to deaths at any year prior to age 39 than afterward, with the death of a newborn weighted at 33 DALYs and the death of someone aged 5 to 20 weighted at approximately 36 DALYs.

Frequently Asked Questions

Who created the DALY metric

The DALY was first developed by Christopher Murray and Alan Lopez as part of the Global Burden of Disease study carried out with the World Health Organization and the World Bank.

How is a DALY different from a QALY

A DALY measures healthy years lost to disease, disability, or early death, while a Quality Adjusted Life Year measures healthy years gained, so the two are used for different sides of health assessment.

What does a lower DALY figure indicate

A lower DALY figure generally indicates a smaller burden of disease, meaning fewer years of healthy life are being lost across a given population.

Why is the DALY sometimes considered controversial

It is considered controversial partly because social weighting and age based valuation assign different worth to years of life at different ages, which raises ethical concerns.

How do public health agencies use DALYs

Agencies use DALYs to compare the impact of different diseases, set health priorities, allocate resources, and evaluate the effectiveness of interventions over time.

What is the difference between YLL and YLD

YLL stands for Years of Life Lost to premature death, while YLD stands for Years Lived with Disability, and adding the two together produces the DALY.

Can DALYs be used to compare countries

Yes, DALYs allow researchers to compare disease burden between countries and regions using a common unit, though differences in data quality can affect the results.

Insights, Analysis, and Developments

Editorial Note: What makes the DALY both powerful and contested is its willingness to assign a numerical value to time spent in poor health, a choice that surfaces uncomfortable questions about how society ranks one life year against another. The formula itself, W = 0.1658 Y e-0.04 Y, embeds judgments about productivity and investment, giving greater weight to deaths before age 39 and treating the death of a newborn as 33 DALYs while a child aged 5 to 20 registers near 36, figures that carry real consequences when they steer funding and policy toward some conditions over others. Disability advocates in particular have reason to scrutinize a system that historically undervalued years lived with impairment, and readers weighing these numbers should keep in mind that the metric remains a tool shaped by human assumptions rather than a neutral yardstick of worth.

Author Credentials: Ian is the founder and Editor-in-Chief of Disabled World, a leading resource for news and information on disability issues. With a global perspective shaped by years of travel and lived experience, Ian is a committed proponent of the Social Model of Disability-a transformative framework developed by disabled activists in the 1970s that emphasizes dismantling societal barriers rather than focusing solely on individual impairments. His work reflects a deep commitment to disability rights, accessibility, and social inclusion. To learn more about Ian's background, expertise, and accomplishments, visit his full biography.