This paper studies how behavioral responses to the Earned Income Tax Credit (EITC) aect the program’s budgetary cost. The EITC encourages labor supply and increases income, thereby reducing public assistance payments to households and increasing taxes paid by households. These sources of revenue reduce the EITC’s net cost. We use administrative Internal Revenue Service tax data linked to Current Population Survey data on enrollment in public assistance programs to estimate the EITC’s net cost. The evidence from three decades of EITC policy expansions implies that the EITC decreases public assistance received by mothers and increases payroll and sales taxes paid. Our estimates suggest that the EITC has a self-nancing rate of 87 percent, so that the EITC’s true cost is only 13 percent of the sticker price. Although the EITC is one of the largest and most important public assistance programs in the U.S., we show that the EITC is actually one of the least expensive anti-poverty programs in the U.S., costing taxpayers about half as much as the school lunch and breakfast programs.