Which countries have already passed peak population, and when will the rest do so?

A peak population occurs when a country’s total number of inhabitants reaches its highest point and then begins to decline permanently. This decline is not temporary, like during a war or famine, but a long-term trend driven by consistently low birth rates. For example, in 2026, 64 countries and territories had already passed this peak, according to United Nations estimates. Most of these countries are in Europe and East Asia, where birth rates have dropped sharply over decades. Some countries, like Japan and Italy, reached their peak population more than ten years ago, while others, such as Thailand and Uruguay, have only recently passed it. The decline is structural, meaning it is expected to continue unless birth rates rise significantly or immigration increases.

Populations shrink when the number of births is lower than the number of deaths over a long period. This happens when the fertility rate—the average number of children born per woman—falls below the replacement level of 2.1 children per woman. Replacement level is the number needed for a population to remain stable without migration. Many countries in Europe and East Asia have fertility rates well below this level. For instance, South Korea’s fertility rate is below 1.2, and Thailand’s is around 1.2. When fertility rates stay low for decades, fewer young people enter the workforce, leading to an aging population and eventual decline. Migration can offset this decline, but in many cases, it is not enough to prevent shrinking populations.

As of 2026, 64 countries and territories have already passed their peak population, according to UN projections. Almost all of these countries are in Europe and East Asia, where fertility rates have been low for decades. For example, Italy peaked in the early 2000s, and Japan’s population started declining around the same time. Other countries, like South Korea and China, are expected to see their populations halve by the end of the century if current trends continue. Some countries in other regions have also passed their peak, such as Uruguay in South America, where the fertility rate is now 1.4, and Thailand in Southeast Asia, where it is below 1.2. These declines are structural and driven by long-term low birth rates.

By the end of the century, many more countries are expected to pass their peak population. According to UN projections, much of South America could peak by the 2050s, and South Asia, including India, may follow by the 2060s. These projections are based on the UN’s medium variant, which assumes moderate changes in fertility rates, life expectancy, and migration. For example, India’s population, currently the world’s largest, is projected to peak around the 2060s before declining. The declines could be substantial: South Korea’s population could shrink by more than half, Italy’s by over 40%, and Spain’s and Thailand’s by about a third. These projections are not certain, as they depend on assumptions that may change over time.

Migration plays a critical role in whether a country’s population grows, stabilizes, or shrinks. Many high-income countries, like the United States, currently have stable or growing populations because of immigration. Without immigration, the US population would peak soon and shrink by 60 million by 2100, according to UN projections. In contrast, countries like Japan and Italy have little immigration and face inevitable population decline. Migration can temporarily offset low birth rates, but it is not a permanent solution. For example, if the US had zero migration, its population in 2100 would be 130 million smaller than if current immigration levels continued. This highlights how sensitive population projections are to assumptions about future migration patterns.