The Best of Seven Reminder Campaigns Raised One-Time Savings Transfers by 0.13 Points

The claim under test is the one behind most reminder features: people fail to save, exercise or show up mainly because they forget, so remind them. Milkman and 19 co-authors put it to a 1.9-million-customer test (PNAS Nexus, 2025). They randomly assigned 1,925,785 customers of a large US bank to eight conditions of about 240,700 each: seven two-month email campaigns running March to April 2022, and one group that got nothing.

The best campaign, weekly savings reminders, raised one-time transfers into savings by 0.13 percentage points, a relative lift of 1.32% (95% CI 0.073 to 0.177 points). The weekly wisdom boxes managed 0.09. Across all seven campaigns together the lift was 0.05 points. At 0.13 points, that is roughly one extra customer in 770 making a one-time transfer.

Recurring transfers, the behavior that builds savings over years, showed no significant effect for any campaign. Savings balances, the main outcome, showed no significant effects either under the authors’ preregistered 1st/99th-percentile winsorization (best campaign +$3.85 a month, adjusted p = .672). Under a far more aggressive 10th/90th-percentile trim, which the authors call particularly aggressive, the best campaign showed an extra $2.33 a month (adjusted p = .026), though the F-test across campaigns for that outcome gave p = .253. For one-time transfers the campaigns did differ from each other (p < .001). The pooled effect was still 0.08 points a month after the emails stopped (p = .004); by months two and three it had dropped below significance. The effect did not differ significantly across 37 customer characteristics.

Scale still pays. The authors extrapolate $6.1 million to $9.9 million in extra savings (using James-Stein shrinkage) if the best campaign reached everyone in the megastudy population, and they call email messaging nearly free. That is a good result for a bank. It is a poor result for the idea that a nudge on its own carries a habit.

Megastudies exist partly to answer the worry that published nudge results are cherry-picked, a problem covered in the piece on publication bias, since every campaign is reported here, hits and misses. Two cautions. The best campaign differed from the others in both frequency and content, so nobody can say which mattered. And the study measured eight weeks of one savings behavior at one bank, so the 0.13 figure is the best of seven, not a general rate for reminders. Reminders do their job when memory is the problem, as the research on offloading to phones suggests; where the problem is follow-through, 0.13 points is what the best of seven emails bought.