Seasons of Birth

Seasons of Birth

Have you ever noticed more birthdays at certain times of the year? Perhaps you recall when you were surprised by lots of birthday invitations or remember being peppered by your favourite social media platform to send birthday messages in a particular month. This phenomenon isn’t random - there is an annual pattern in birth rates.

Around the world, birth rate peaks and dips follow an annual pattern often tied to environmental, social, and cultural factors. In Australia, these patterns are shaped by unique geographical and climatic conditions along with policies and societal norms. While much of the conversation around fertility focuses on declining birth rate trend(s), seasonal patterns are often less discussed, yet they have potentially significant implications for public health, businesses and policy planning.

When are most babies born?

Globally, patterns differ depending on geography and culture. In Europe and North America, births often peak in spring or autumn, while tropical regions exhibit less pronounced patterns presumably associated with consistent climates (Cancho-Candela et al., 2007; Russell et al., 1993).

Australia’s vast geographic diversity, from the tropical north to the temperate south, is an interesting case study. Regions like Victoria and Tasmania show springtime peaks (September-October), while tropical northern areas experience peaks in late summer and early autumn (February-April).

In the mid-20th century, Australian families often timed pregnancies around harvest seasons (Mathers & Harris, 1983). Over time, however, as urbanisation took hold, healthcare advanced and contraceptives became more accessible, these patterns started to shift. Today, we observe gentle seasonal peaks in birth rates, though nowhere nearly as pronounced as in previous decades.

Temperature plays a surprising role in birth seasonality (Barreca et al., 2018). In Australia’s tropical north, wet conditions can disrupt everyday life, indirectly shaping when couples conceive (Wilson, 2020). In contrast, temperate regions like Victoria enjoy milder conditions, which results in less seasonal spikes. Another important factor is daylight length or photoperiod. Research in from multiple countries have found that longer days often coincide with higher conception rates (Russel et al., 1993). 

Map of Australia showing geographical patterns of birth seasonality

Note: Adapted from the geographical patterns of birth seasonality in Australia by Wilson, T., McDonald, P., & Temple, J. (2020). The geographical patterns of birth seasonality in Australia. Demographic Research, 43, 1185–1198. https://doi.org/10.4054/DemRes.2020.43.40). Copyright 2020 by Springer. Birth Index calculated using ABS births data.

So why does it matter?

Whilst there is no study that we are aware of that has mapped the pros and cons of being born in particular months (and note these will differ according to location) some research does hint at intriguing links. For instance, birth timing has been connected to diseases like measles and asthma – possibly because maternal immunity fluctuates throughout the year (Martinez-Bakker et al, 2014; Almqvist et al., 2020). Summertime arrivals might face higher pollen exposure, potentially elevating asthma risks, while winter babies could encounter vitamin D deficiencies.

Birth month also intersects with education and sports through what is known as the Relative Age Effect (RAE) - children born earlier in a school or sports selection period often enjoy developmental advantages over their younger peers (Cobley et al., 2009; Barake et al., 2023). Put simply, if you’re older when school starts, or a sports season kicks off, you may be taller, stronger, or more cognitively prepared than classmates born later in the same year (Leigh & Ryan, 2008). 

Interestingly, the season of birth doesn’t just shape health and academic outcomes. Research suggests it might even influence professional trajectories (Buckles & Hungerman, 2013). What’s behind this connection? One recent explanation for this link is that babies born at different times of the year are conceived by mothers with distinct socioeconomic characteristics, implying that who conceives could be as influential as when conception occurs (Dahlberg & Andersson, 2018).

So why does this matter? Well, healthcare systems need to respond to these cyclical birth trends – particularly in anticipating staffing and resource needs. Economically, seasonal ebbs and flows in births can affect labour supply and cash flows which for employers of all sizes and types will require careful planning.

Perhaps the most intriguing implication is that the persistent presence of seasonality reminds us that the decision to have a child is highly complex and determined by an array of social, economic and ultimately biological and environmental factors. Importantly the complex interplay of these factors indicates, and perhaps explain, the limited influence central authorities can have on its population fertility decision making.

Take Australia for example, many policies that may be expected to influence the decision to have a child over recent decades have changed, yet seasonality has remained.  Despite policies such as the Baby Bonus, Parental Leave and Family Tax benefits, the seasonal rhythm of births remains surprisingly consistent. Researchers have found that these government initiatives, significant though they are, haven't erased the underlying patterns, or dramatically altered overall fertility trends (Drago et al., 2011).

So, if your social media feed is suddenly flooded with “gender reveals” next month, don’t be surprised. The decision to have a child is influenced by a mix of biological, social and personal factors that even parents might struggle to fully explain. Despite changing policies and societal shifts, the rhythms of birth seasonality remind us that some patterns are remarkably enduring.

Authors: Sarah Sinclair, Alicia Bubb, Jonathan Boymal and Ashton de Siva

25 February 2025

Share

25 February 2025

Share

Engage

Related News

Hands holding a baby's feet

Seasons of Birth

Have you ever noticed more birthdays at certain times of the year? Perhaps you recall when you were surprised by lots of birthday invitations or remember being peppered by your favourite social media platform to send birthday messages in a particular month. This phenomenon isn’t random - there is an annual pattern in birth rates.

A person donating blood

Engaging Generation Z: Overcoming Barriers and Building a Sustainable Blood Donor Base for Lifeblood

The Australian Red Cross Lifeblood aims to address a critical challenge in sustaining a volunteer donor base by understanding the motivations and barriers that influence blood donation. While existing research identifies factors like attitudes, perceived behavioural control, and donation anxiety as predictors of donor intentions, these studies largely overlook the 18–30-year-old cohort—a group with beliefs and behaviours distinct from older donors.

employer-surveillance-header-1.jpg

Does tracking your employees actually make them more productive?

Should employers prioritise efficiency at all costs? It might seem like a good idea. More processes than ever before can now be automated with robotics, artificial intelligence and other technology.

clothes-pile-header.jpg

Gen Z supports sustainability – and fuels ultra-fast fashion. How does that work?

Generation Z has been called “the sustainability generation”. Born between 1997 and 2013, 58% of this consumer cohort seek to buy products that are sourced sustainably. Australian Gen Zs say they are willing to pay more for brands that have a positive impact on society.

Load more +
aboriginal flag
torres strait flag

Acknowledgement of Country

RMIT University acknowledges the people of the Woi wurrung and Boon wurrung language groups of the eastern Kulin Nation on whose unceded lands we conduct the business of the University. RMIT University respectfully acknowledges their Ancestors and Elders, past and present. RMIT also acknowledges the Traditional Custodians and their Ancestors of the lands and waters across Australia where we conduct our business - Artwork 'Sentient' by Hollie Johnson, Gunaikurnai and Monero Ngarigo.

More information