We study gender gaps across two central domains of household finance: stock market participation and mortgage borrowing and refinancing. Using rich microdata, we show that these gaps are small among lower-income, less-educated households but widen sharply at higher socioeconomic status, with women participating less in the stock market, borrowing on less favorable terms, and refinancing less optimally than comparable men. Financial literacy grounded in quantitative reasoning explains much of this gradient. Leveraging within-family sibling comparisons, we trace the gaps to childhood differences in math skills and math-related attitudes shaped by persistent gender stereotypes.