Drawing on long-term data on mortality and longevity, researchers from the Imperial College London and the World Health Organization (WHO) have predicted the average life expectancies for people in 35 countries born in 2030. Residents of every country in the study can expect to live longer, with South Korean women topping the list at 90 years – but it's not such great news for the US.

The 35 countries in the study were chosen because they all had reliable mortality data dating back at least 30 years, and included high-income countries like the US, UK, Canada, and Australia, as well as emerging economies like Poland, Mexico and the Czech Republic.

Starting from that historical data, the researchers developed a new method for forecasting how those trends would continue into the future. The figure is calculated by looking at the age of death, by any cause, across a nation's entire population, meaning medical advances alone don't always account for improvements: for example, violence and accidents that take the lives of younger people can skew a country's average downwards.

Increases in life expectancy were seen across the board, but the average age of death and the rate of improvement varied by region. A baby girl born in South Korea in 2030, for example, could expect to live to the ripe old age of 90.8 years, while the average South Korean man should reach 84.1.

Australian and Swiss men born in 2030 can expect to hit 84, with Canada and the Netherlands trailing just slightly behind, at 83.9 and 83.7 respectively. After South Korea, French women should be the next longest-living at 88.6 years, followed closely by women in Japan at 88.4, Spain at 88.1 and Switzerland at 87.7 years.

"We repeatedly hear that improvements in human longevity are about to come to an end," says Majid Ezzati, lead researcher on the study. "Many people used to believe that 90 years is the upper limit for life expectancy, but this research suggests we will break the 90-year-barrier. I don't believe we're anywhere near the upper limit of life expectancy – if there even is one." Interestingly, other studies have suggested that the upper limit could be 125 years.

The new research also found that in 2030, people over the age of 65 will generally live longer than people of the same age do today. A South Korean woman who turns 65 in 2030 should live another 27.5 years, with French women the same age living a further 26.1 years, and Japan, Spain and Switzerland following close behind. Men of that age in 2030 were longest-living in Canada (an extra 22.6 years), New Zealand (22.5), Australia (22.2), South Korea (22) and Ireland (21.7).

"The increase in average life expectancy in high income countries is due to the over-65s living longer than ever before," says Colin Mathers, co-author of the study. "In middle-income countries, the number of premature deaths – i.e. people dying in their forties and fifties, will also decline by 2030."

So why have figures from the US been conspicuously absent so far? Unfortunately, the researchers point out that Americans born in 2030 are predicted to have the lowest life expectancy among developed countries – 83.3 years for women and 79.5 for men. A lack of universal healthcare poses a problem, as does unusually high rates of child and maternal mortality, homicide and obesity.

"The fact that we will continue to live longer means we need to think about strengthening the health and social care systems to support an aging population with multiple health needs," says Ezzati. "This is the opposite of what is being done in the era of austerity. We also need to think about whether current pension systems will support us, or if we need to consider working into later life."

The research was published in The Lancet.