Imran Hossain, a private-sector employee in Dhaka, sat in his rented flat last month and tallied the costs of a second child. He and his wife already had one; they wanted another, but the arithmetic unsettled him. Doctor’s visits, hospital fees, infant formula, nappies, and later school fees—all on a salary that would not stretch. “If we have another child, expenses will jump,” he said, “but my pay won’t. I lie awake wondering whether I can raise two children properly.” His private reckoning, recorded by a local newspaper, is a small, sharp instance of a calculation being made in kitchens and rented rooms across the world.

That calculation now has a global statistical portrait. To mark World Population Day, the UN Population Fund released a survey of more than 108,000 people aged 18 to 39 in 73 countries, from Italy to Bangladesh, Argentina to India. The findings are a study in paradox. Two-thirds of young adults feel positive about the future; more than two-thirds want to marry. Eight in ten say the joy children bring is the most important reason to become a parent. Yet 88 per cent see financial security as a prerequisite, 87 per cent cite stable employment, and more than half identify the cost of living and housing as the main obstacles. The desire for family is not vanishing; it is being postponed, often indefinitely, by a ledger that does not balance.

In Latin America, the ledger is tilting fast. A long-running survey by the Universidad Austral in Argentina found that the share of people who consider having and raising children “very important” for a fulfilling life fell from 77 per cent in 2015 to 46 per cent this year. Among those aged 18 to 34, only one in three now holds that view. The majority of Argentines who do not want children say simply that parenthood is not part of their life plan. In Mexico, specialists at the National Autonomous University point to a similar shift: young people cite climate change, economic precarity, and the desire for other experiences. “I don’t want to be a mother because of the global context—hunger, the economy, climate change,” one graduate student told researchers. The decision, once a near-automatic step into adulthood, now competes with professional development, mobility, and personal wellbeing.

Viewed from Milan, the same pressures are reshaping the European family. Demographer Letizia Mencarini of Bocconi University notes that the UN survey reveals a striking uniformity: young women, more than men, refuse to have children until they have stable work, fearing that care will fall entirely on them. In Italy, the middle class is particularly squeezed; both the very poor and the very rich now have more children than those in between. “What young people lack is a house and an income to start a family,” Mencarini says. In Bangladesh, the dynamic is different but equally troubling: the fertility rate has edged up to 2.4 children per woman, a rise that experts attribute to a decade of weakening family planning services, vacant posts, and scarce contraceptives. The country that once won international praise for reducing fertility now sees its gains at risk, even as half of all girls still marry before 18.

In Tehran, a different debate is unfolding. New research suggests that the economic burden of ageing populations may be less catastrophic than long feared, because technology is slowing the growth of health costs and older people are staying healthier for longer. Yet the global survey makes plain that the young are not waiting for actuarial reassurances. They are looking at their pay slips, their rent, and the state of the world, and making a private arithmetic. In a rented flat in Dhaka, a father stares at a ceiling; in a Buenos Aires café, a young woman scrolls past job listings; in Mexico City, a student lists the reasons she will not bring a child into a warming world. The joy they all acknowledge is real, but the price, for now, is too high.