In the United States, 24% of adults have no savings and 39% have less than a month of income saved. We present results from a megastudy where nearly 2 million customers of a US bank were randomly assigned to receive one of seven different 2-month email campaigns, each employing a different behavioral science insight to nudge one-time and recurring savings deposits and increase savings balances or to a control condition without such messages. These campaigns increased the probability of making a one-time savings deposit, on average, by 0.05 percentage points (a 0.51% increase over control). The best-performing campaign delivered weekly messages to customers that differed depending on recent savings behavior: messages to customers who had not made a savings account deposit in the last week included a simple reminder to save, while those to customers who had made a savings account deposit in the prior week were congratulated on this accomplishment. This top-performing campaign increased the monthly likelihood that a customer made a one-time savings deposit by 0.13 percentage points (a 1.32% increase). We estimate that rolling this 2-month campaign out to everyone in our megastudy population would have led to an extra $6,123,996 to $9,910,090 in savings. Together, our findings highlight that light-touch, frequent email nudges can cost-effectively create small increases in savings deposits in the United States. Ideally, to generate meaningful benefits, behavioral science insights would be incorporated into a wider range of communications and incentives designed by financial institutions.