This article introduces collective rationality and comparative advantage into understanding household financial decision-making responsibility allocation and its relationship to wealth accumulation. Evidence from the Health and Retirement Study (HRS) shows that conscientiousness, memory, and numeracy are favorable personal attributes for household financial decision-making. Greater relative advantages in these attributes predict a higher probability of assuming financial responsibility. Households that assign the disadvantaged spouse as the financial decision-maker tend to have a lower total net worth and a lower financial net worth. Our results suggest that it is critical for financial planning professionals to engage both spouses in the initial discussion of household finances and to assess the efficiency of the status quo financial decision-making responsibility allocation.