This paper studies the direct and indirect effects of nudging, by means of a field experiment with a financial management platform in Brazil. Reminders for upcoming credit card payments reduced credit card late-payment fees by 14%, but increased overdraft fees in checking accounts by 9%. The unintended effect is concentrated in users with a history of overdraft use. These users experienced a net increase of 5% in total fees, while the rest experienced savings of 15%. The results provide clear insights for nudge design: like any policy action, nudges can have side effects, and one size may not fit all.

Using an experiment in which 3.1 million bank customers were encouraged to save, we explore the mechanisms behind coholding liquid savings and credit card debt. Theoretically, we show that the joint responses of spending, saving, and borrowing to the nudge differ across economic models of coholding. Using machine learning techniques, we find that the most responsive individuals reduce spending and increase savings by 4.9% (206 USD PPP per month) while their credit card debt remains unchanged. These individuals' marginal responses to the nudge are consistent with our model of coholding for the purpose of self‐ or partner‐control.

During the first half of 2020, the difference in savings from mortgage refinancing between high- and low-income borrowers was 10 times higher than before. This was the result of two factors: high-income borrowers increased their refinancing activity more than otherwise comparable low-income borrowers and, conditional on refinancing, they captured slightly larger improvements in interest rates. Refinancing inequality increases with the severity of the COVID-19 pandemic and is characterized by an underrepresentation of low-income borrowers in the pool of applications. We estimate a difference of $5 billion in savings between the top income quintile and the rest of the market.