In the UK the gender pay gap on entry to the labour market is approximately zero but ten years after labour market entry, there is a gender wage gap of almost 25 log points. This article explores the reason for this gender gap in early-career wage growth, considering three main hypotheses – human capital, job-shopping and ‘psychological’ theories. Human capital factors can explain about 11 log points, job-shopping about 1.5 log points and the psychological theories up to 4.5 log points depending on the specification. But a substantial unexplained gap remains: women who have continuous full-time employment, have had no children and express no desire to have them earn about 8 log points less than equivalent men after 10 years in the labour market.