tempo effects — Alpha.Sources

Freeze the eggs!

Global birth rates are falling at an accelerated pace. According to the UN, the global total fertility rate (TFR) dropped to a record low of 2.25 in 2023 and is projected to fall further to 2.2 in 2024. At this pace, the TFR is set to dip below the replacement level of 2.1 nearly two decades earlier than the UN’s latest forecasts had anticipated.

The long-run decline in fertility has two main components. The first is the "quantum effect"—the trend for families to have fewer children as incomes rise, choosing instead to invest more in each child, particularly through education. Economics and evolutionary theory both rely on this shift in the quantity-quality trade-off to explain why fertility has fallen since the Industrial Revolution, even as wealth has grown.

The second component is the "tempo effect"—birth postponement. Women are delaying motherhood due to rising labour force participation and career opportunities, which increase the opportunity cost of having children, and shifting social norms. Other contributors include difficulty in finding a partner, precarious housing and job markets, and evolving personal preferences. Meanwhile, outright childlessness is increasing, which neither the quantum nor tempo frameworks fully explain.

Demographicsclaus vistesenMay 24, 2025Fertility, IVF, egg freezing, demographics, birth rates, te, tempo effects

Falling global fertility, how far and how fast?

It has been a while since I last delved into one of my favorite topics: global demographics. In this piece, I revisit the subject by examining high-level data on key global demographic indicators from the UN’s July 2024 Population Prospects database. I will begin with birth rates.

Scarcely a day goes by without an article, podcast, or both highlighting the accelerating decline in global fertility. As I explain in my essay on the fertility wars, this discussion tends to divide interlocutors into two increasingly polarized factions. On one side are those who believe falling fertility is a grave problem; on the other are those who remain more sanguine, viewing declining birth rates as a natural consequence of modernity—or perhaps postmodernism—and less of a threat to economic growth, government budgets, or humanity’s survival. If women choose to have fewer children and prioritize careers and personal freedom—long the exclusive domain of men—shouldn’t we support that choice?

Delayed Gratification - Why are global birth rates falling, and does it matter?

This is the final chapter in the first part of my long-running demographics project. In the previous chapter I described the quantum effect of fertility, which hypothesises a negative relationship between fertility and rising incomes as parents substitute quantity for quality in their reproductive decisions and child-rearing. But can the quantum effect explain why birth rates in one country after the other appears to be stuck below the replacement level, and why global fertility will soon drop below that same level? The answer is no.

To understand current and more recent post WWII global fertility trends—broadly since the 1970s—we need to introduce tempo effects to the analysis. Tempo effects describe the tendency of women to postpone the timing of their first child. By mathematical logic, prolonged tempo effects can drive significant population ageing, but a more fundamental question is whether birth postponement also has a lagged effect on quantum, or more precisely, cohort fertility. This chapter discusses these question in the context of the hypothesis of a Second Demographic Transition, SDT, and presents a number of case studies to explore the specifics of recent fertility trends in key countries and regions. The chapter finishes by discussing the idea of a fertility trap, and whether the increasingly accelerating decline in global birth rates are a problem, drawing on the recent polarisation in the debate on this issue.

Japan's disappearing population

Japan invariably looms as the central case study for the economic and societal effects of rapid fertility decline, population decline and ageing. Japan is, measured by median age, the oldest country on earth, excluding the greying millionaires of Monaco and the some-5,000 people on British St. Helena. At the end of 2021, Japan had a median age of 48.4, well ahead of the second major country on the list, Italy, with a median age of 46.8. Japan is about to get older still. According to preliminary estimates, the country’s fertility rate fell further last year, albeit marginally, while the gap between births and deaths remained wide as ever. The number of live births fell by 5.0%, to 770.774, while deaths rose by 9.0%, to 1.57 million. Japan’s rapidly ageing population is the result of a quicker and more sustained post-1945 fertility transition than in other developed economies.

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