While gender gaps in average math performance are now close to zero in developed countries, women are still strongly underrepresented among math high performers (1). This gender gap contributes to the underrepresentation of women in math and science in higher education and to their subsequent worse position in the labor market (2, 3). With the roles of nature and nurture (4–6) on gender performance gaps having been debated for more than a century, research in the 1990s and 2000s (7–9) suggested a cultural origin, relating gender gaps in math to measures of countries' gender inequality. However, with more recent studies (10–12) having shown that this relation is weak, today we have no clearly identified relationship between countries' socioeconomic or cultural environment and the gender gap in math. We relate below gender gaps in math to societal inequalities that are not directly related to gender. We find a strong and robust relationship and provide tests suggesting that it is causal: Countries that are generally more egalitarian, or that have institutions more conductive to equality, have a lower gender performance gap in math, suggesting that this gap is partly shaped by more general societal inequalities.