The UK’s placing is one lower than last year’s league table and seven down on 2020’s list.
Finland topped the annual ranking for the seventh year in a row, followed by Denmark, Iceland, Sweden and Israel.
Meanwhile, Afghanistan was classed as the least happy country, after Lebanon, Lesotho, Sierra Leone and the Democratic Republic of the Congo.
The annual World Happiness Report is based on data from Gallup, analysed by a global team led by the University of Oxford.
People in 143 countries and territories are asked to evaluate their life on a scale from zero to 10, with 10 representing their best possible life.
Results from the past three years are averaged to create a ranking.
For the first time, experts analysed rankings by age group, which often found a marked difference in how happy young and older people are.
In many European countries, such as the UK, Norway, Sweden, Germany, France, and Spain, the old were found to be significantly happier than the young,
The drop in wellbeing for under-30s also caused the US to fall out of the top 20 for the first time since the World Happiness Report was first published in 2012.
Experts found that overall those born before 1965 are, on average, happier than those born since 1980.
Among millennials, life satisfaction tends to drop with each year of age, while among “boomers” life satisfaction increases with age, the research found.
Professor Jan-Emmanuel De Neve, Director of Oxford’s Wellbeing Research Centre, said it meant that some children and adolescents were essentially experiencing the “equivalent of a mid-life crisis”.
“Piecing together the available data on the wellbeing of children and adolescents around the world, we documented disconcerting drops especially in North America and Western Europe,” he said.
“To think that, in some parts of the world, children are already experiencing the equivalent of a mid-life crisis demands immediate policy action.”
