Completed Cohort Fertility Rates

This article examines completed cohort fertility rates, a measure of the average number of children per woman among women born in the same year.

Released
24/07/2026
Release date and time
24/07/2026 11:30am AEST

This article uses the demographic definition of 'fertility' which refers to:

  • the number of live births per woman
  • the number and prevalence of live births produced by a population.

Kippen (2019)

Births are the starting point of the life cycle, and have a key role in how populations change. Alongside deaths and migration, they shape the size and composition of populations over time. Births are the events, and fertility is the frequency of those events among the female population.

Patterns of fertility can change from one generation of women to the next, influenced by social, economic and cultural factors. To understand these longer-term shifts, demographers use multiple measures of fertility that look beyond births in a single year and examine childbearing across a lifetime.

There are many ways to measure fertility, including when people have children and how many children they have. In Australia, the timing of childbearing has shifted over recent decades, with parents having children at older ages than in the past. Between 1975 and 2024, the median age of parents increased from 25.8 to 32.1 years for mothers and from 28.6 to 33.9 years for fathers. While measures such as median age describe the age parents are when they have their children, completed cohort fertility rates measure the average number of children women have over their lifetime.

This article will explain how to compare completed cohort fertility rates across time and with other fertility measures including total fertility rate.

Measures of fertility

Completed cohort fertility rate

Total fertility rate

Comparing measures

The key difference between cohort and period fertility measures lies in timing and interpretation.

  • Total fertility rate (TFR) is the average number of children a woman is expected to have over her lifetime, from age 15 to 49 years, if the current age-specific fertility rates (ASFRs) remain the same. It is a period measure as it uses one year of births for many groups of women.
  • Completed cohort fertility rate (CCFR) measures the total number of children women have from age 15 to 49 years. It is a cohort measure because it uses many years of births for one group of women.

 

Table 2: Comparison between completed cohort fertility rate and total fertility rate
MetricCompleted cohort fertility rateTotal fertility rate
TypeCohort basedPeriod based
Time variableBirth year of the motherRegistration year of a birth
Time frameLifetime (up to age 49 years)Single calendar year
PopulationWomen born in same yearWomen aged 15-49 in single year
Sensitivity to timingLowHigh
UsefulnessLong-term trendsShort-term fluctuations

TFR and CCFR often tell different stories because they measure fertility at different points in time. For example:

  • The cohort of women aged 49 in 2024 had a CCFR of 2.02 children per woman.
  • The TFR in 2024 was lower at 1.48 children per woman.

CCFR and TFR can be compared during the cohort's childbearing years to understand the differences between the measures. Because CCFR is calculated at age 49, this is several years after most children are born, so it can be helpful to compare CCFR with the TFR in the year the cohort is at the highest fertility. The following graph uses age 30, as this is close to the median age of mothers across the time series. 

 

  1. CCFR year is shown as the year the cohort is aged 30

Age of mothers

The median age of mothers has changed over time. It was 28.2 years in 1945, lowered to 25.8 years in 1975, and then increased to 32.1 years in 2024.

Fertility at age 30 provides a useful indicator of more recent shifts in family formation. As CCFR is the sum of age-specific fertility rates, we can compare fertility at different ages during the cohort's reproductive years.

Women born in 1915 and 1945 had a similar total number of children, with a CCFR of 2.43 and 2.49 children per woman, respectively. Women born in 1975 had fewer children than earlier generations, with a CCFR of 2.02 children per woman. However, the age at which women had their children differed across these generations.

The CCFR can be broken down by the age of the mother when her children were born. Women born in:

  • 1915 had an average of 1.38 children before age 30 and 1.05 children at age 30 and over, indicating childbearing was relatively evenly split across these age groups
  • 1945 had most of their children at younger ages, averaging 1.99 children before age 30 and 0.51 children at age 30 and over
  • 1975 had fewer children overall and were more likely to have them later in life, averaging 0.94 children before age 30 and 1.08 children at age 30 and over.

Fertility among women aged under 20 years remained relatively low across cohorts, at less than 0.25 children per woman on average.

 

Age-specific fertility rates

Age-specific fertility rates (ASFRs) are a component of both CCFR and TFR as they are the measure of births per thousand women of a given age. These can be viewed over the reproductive years of a cohort using CCFR or over a range of ages in a single year using TFR. For more information, see Methodology.

ASFRs can be used to understand fertility patterns as the births are registered and before a generation has completed its reproductive years, as CCFRs are calculated after a cohort reaches age 49.

The following graph shows ASFRs for the year the births were registered and the age group of women at the time of the birth.

ASFRs declined across most age groups of women during the 1970s, followed by a gradual increase in fertility among women aged 30 to 34 and 35 to 39, compared with women aged 20 to 24 and 25 to 29.

Abbreviations

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Glossary

Glossary

References

References

Methodology

Methodology

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