Bairoh and her colleagues analysed the full population of Finnish STEM degree holders aged 30 to 40 across five birth cohorts, from those born in 1960 to those born in 1980. Instead of focusing on hourly wages, the researchers examined total annual income, including earnings and taxable benefits such as parental leave. This approach makes it possible to see how careers unfold over time, and how life events like having children or living with a partner shape financial outcomes.

The results are striking. Across every cohort, women earned less than men, and the gap did not shrink for younger generations. In most cohorts, women’s total annual incomes hovered at roughly 70–80% of men’s, with little sign of convergence among those born more recently. Importantly, women’s share of STEM degree holders rose from 14% in the 1960 birth cohort to 24% in the 1980 cohort – yet this increased representation did not translate into income parity.

Economic conditions also mattered. Men’s incomes rose particularly quickly during periods of economic growth, creating what the researchers describe as a “male boost”, while economic downturns left lasting scars, especially for those whose careers began during recessions.

Family life played a major role in reinforcing these differences. Consistent with earlier research, Bairoh and her colleagues’ study found a clear motherhood penalty: women’s incomes dropped after the birth of a child and did not fully recover over time. By their late thirties, mothers’ earnings trajectories remained roughly 20–30% below those of comparable men.

The study also uncovered an unexpected pattern among men living alone, whose incomes grew more slowly than those of men living with a partner – a “living-alone penalty” that did not apply to women.

The findings challenge the idea that increasing the number of women in STEM is enough to close the gender pay gap. As Bairoh and her colleagues show, deep-rooted gender norms around work, family and relationships continue to shape who is rewarded in the labour market. Even in one of the world’s most equality-oriented societies, equal education does not yet translate into equal income.