Birth Rates, Death Rates, and Natural Population Change

The birth rate is the number of live births per 1,000 people per year, the death rate is the number of deaths per 1,000 people per year, and natural population change is the difference between them, which can be expressed per 1,000 or as a percentage. In brief: natural change = birth rate − death rate. A country with 30 births and 10 deaths per 1,000 people grows naturally by 20 per 1,000, which is 2.0% per year. Total population change also includes migration.

These simple rates show whether a population is growing, stable or shrinking, and they help planners estimate the need for schools, hospitals and pensions. This guide explains how to calculate the rates, what influences them, how natural change is linked to migration and doubling time, compares high and low rates, works through examples, outlines the history of the measurement and corrects common mistakes.

How are birth and death rates calculated?

The crude birth rate (CBR) is the number of live births in a year divided by the total population and multiplied by 1,000. The crude death rate (CDR) is calculated in the same way using the number of deaths. They are called “crude” because they use the whole population and do not take account of age structure.

Related measures are the total fertility rate (TFR), the average number of children a woman would have in her lifetime at current rates, the infant mortality rate, the number of deaths of babies under one year per 1,000 live births, and life expectancy, the average number of years a newborn is expected to live. A TFR of about 2.1 is called the replacement level in countries with low mortality, because it keeps the population stable in the long run.

How is natural population change calculated?

Natural change (also called the natural increase rate) is the CBR minus the CDR. The result is per 1,000 people. Dividing it by 10 gives a percentage.

• If births exceed deaths, there is natural increase and the population grows.
• If deaths exceed births, there is natural decrease and the population shrinks, as in Japan and several countries in eastern and southern Europe, where migration may offset the loss.
• If they are equal, the population is stable.

The overall change in population also depends on net migration (immigrants minus emigrants). So: total change = natural change + net migration. The doubling time of a growing population can be estimated with the rule of 70: years to double ≈ 70 ÷ growth rate in percent.

What affects birth rates?

Birth rates are higher where children contribute to family income, where infant mortality is high so parents have more children to ensure that some survive, where contraception and family planning are limited and where girls have little education. Cultural and religious beliefs and government policy also matter. Birth rates are lower where women are educated and employed, children are expensive to raise, marriage is later and pensions and healthcare reduce the need to rely on children in old age. Urban living also tends to reduce family size.

What affects death rates?

Death rates fall with better medical care, vaccination, clean water, sanitation, nutrition, housing and education. They rise because of famine, war, epidemics and natural disasters. A surprising point is that a rich country can have a higher crude death rate than a poor one, because its population is older. For example, a country with many elderly people may have a CDR of 10 or more, even with excellent healthcare, while a young population in a poorer country may have a lower CDR.

High and low rates compared

Worked example: rates, growth and doubling

1. Calculating rates: a country has 5,000,000 people, 120,000 births and 45,000 deaths in a year. CBR = 120,000 ÷ 5,000,000 × 1,000 = 24. CDR = 45,000 ÷ 5,000,000 × 1,000 = 9.
2. Natural change: 24 − 9 = 15 per 1,000, which is 15 ÷ 10 = 1.5% per year.
3. Number of people: 120,000 − 45,000 = 75,000 more people from natural change. Check: 1.5% of 5,000,000 = 75,000.
4. Adding migration: if 10,000 more people arrive than leave, the total change is 75,000 + 10,000 = 85,000, so the population becomes 5,085,000, a growth of 1.7%.
5. Doubling time: at 1.5% growth, the doubling time is about 70 ÷ 1.5 = 47 years. At 3% it would be about 70 ÷ 3 = 23 years.
6. Natural decrease: a country with CBR 7 and CDR 12 has natural change of 7 − 12 = −5 per 1,000, or −0.5% per year.

How did population rates change over time?

Before the 18th century, both birth and death rates were high, so populations grew slowly. As public health, food supply and medicine improved first in Europe, death rates fell, while birth rates stayed high for a time, causing rapid growth. Later birth rates also fell. The demographer John Graunt analyzed London’s records of births and deaths in the 17th century, and Thomas Malthus argued in 1798 that population growth would outpace food supply. Since the mid-20th century, death rates have fallen sharply in most developing countries, and global fertility has dropped from around five children per woman in the early 1960s to about two to three today (approximate figures from UN estimates).

Which mistakes are common?

Mistake 1: Forgetting to multiply by 1,000

Birth and death rates are expressed per 1,000, not as a raw fraction. The percentage change is the per-1,000 rate divided by 10.

Mistake 2: Ignoring migration

Natural change alone does not give the total change in population. Net migration must be added.

Mistake 3: Believing that a high death rate means poor healthcare

An older population has more deaths each year, even with very good medical care.

Mistake 4: Mixing up birth rate and fertility rate

The birth rate is births per 1,000 of the whole population. The fertility rate relates births to women of childbearing age or the number of children per woman.