Todd Zywicki:

EVALUATING THE TWO-INCOME TRAP HYPOTHESIS: As I’ve been working on my book on bankruptcy this summer, I’ve been going back through the various hypotheses that have been advanced for the rise in American bankruptcy filings in the 1980s and 1990s. One hypothesis was that advanced in The Two-Income Trap: Why Middle Class Mothers and Fathers are Going Broke by Professor Elizabeth Warren and Amelia Warren Tyagi.
Warren & Tyagi’s argument can be easily summarized. They focus on the rise in the number of households with two parents working as an indication of economic distress. Conventional economic theory would indicate that one benefit of having a second wage-earner is that it will make the family more resilient to a financial setback or loss of job than a traditional family with only one wage-earner. Families today, unlike those a generation ago, can save the second earner’s income as precautionary savings, thereby making it easier to withstand a setback.
So I got out my handy calculator and calculated what the indicated percentage of taxes translates into in terms of actual dollars paid in taxes. In turns out that for the 1970s family, paying 24% of its income in taxes works out to be $9,288. And for the 2000s family, paying 33% of its income (a higher rate presumably because of progressivity hitting the second wage-earners income) in taxes works out to be $22,374.