A quarter of adults struggle to work out how much change they should get in a shop and half cannot read a simple financial line graph, a study suggests.
The study, from Cambridge University and University College London, found "striking weaknesses" in adults' financial skills across 31 countries.
It says financial literacy is essential if consumers are to avoid getting into debt or being misled on money matters.
The report says the findings point to a need for "urgent policy intervention".
The researchers analysed more than 100,000 results from 16- to 65-year-olds from 31 countries (listed below) who had completed the Programme for International Assessment of Adult Competencies test in 2011.
As part of this test, adults were asked four questions that assessed their ability to apply numerical skills to everyday financial tasks.
The researchers' analysis of these results said: "A substantial number of people lack the basic skills that are needed to solve everyday financial tasks."