Weight Watchers starters sustained more warehouse-club spend
Average observed monthly spend in the six months before and after each consumer's Weight Watchers start
Average observed monthly warehouse-club spend
Source: YipitData US credit and debit card panel. 12,700 Weight Watchers starters and 38,103 matched controls. Weight Watchers start cohorts: August 2023-January 2026. Month of start excluded.
Chart data
| Series | Average observed monthly warehouse-club spend |
|---|---|
| Weight Watchers starters: before | $163.89/month |
| Weight Watchers starters: after | $159.40/month |
| Matched controls: before | $161.84/month |
| Matched controls: after | $150.12/month |
How did warehouse-club spending change after consumers started Weight Watchers?
Among 12,700 warehouse-club-active consumers who started Weight Watchers, average observed monthly spend at Sam's Club, Costco, and BJ's declined from $163.89 in the six months before the start to $159.40 in the six months after it, excluding the start month. Spend for 38,103 matched non-Weight Watchers controls declined from $161.84 to $150.12 over comparable windows. The resulting difference-in-differences was positive $7.23 per month.
Did Weight Watchers starters shift their wallet toward Sam's Club?
The evidence points to broader warehouse-club spend retention, not a clear shift toward Sam's Club. Sam's Club spend declined $0.34 per month for Weight Watchers starters and $4.75 for controls, a positive $4.41 difference-in-differences. But average Sam's Club wallet share moved from 44.3% to 43.8% for starters and from 44.3% to 43.1% for controls, only a positive 0.7 percentage-point difference against roughly 47 percentage points of consumer-level variation. Without formal significance testing, that wallet-share result should be treated as effectively null.
What does the pattern imply for the Sam's Club and Weight Watchers partnership?
Sam's Club announced its Weight Watchers collaboration on July 9, 2026, after the measured start cohorts, so this analysis is a pre-partnership behavioral baseline rather than an estimate of partnership impact. Among consumers with no Sam's Club spend in the pre-period, 5.9% of Weight Watchers starters later spent at Sam's Club versus 4.6% of controls, a 1.3 percentage-point directional gap that was not significance-tested. The partnership can now be evaluated against those baseline retention, acquisition, and wallet-share measures as post-launch data accumulates.
Assumptions & Methodologies
This analysis uses observed, unscaled US credit and debit card transactions from January 2021 through July 2026. A Weight Watchers starter is a consumer whose first observed Weight Watchers card transaction occurred from August 2023 through January 2026, with no earlier observed transaction back to the panel floor. Pre-2021 customers who later restarted may therefore be misclassified as new starters.
The study includes consumers with at least one Sam's Club, Costco, or BJ's transaction during the six months before the Weight Watchers start. One consumer active in both treatment and control definitions was removed. Controls had no observed Weight Watchers transactions and were sampled three-to-one within start month, pre-period warehouse-club spend quartile, and prior Sam's Club presence. The matching approach is stratified sampling, not a propensity-score or nearest-neighbor match.
Pre and post measures cover months minus six through minus one and plus one through plus six; the start month is excluded, and zero-spend months remain in monthly averages. Wallet share is Sam's Club spend divided by combined Sam's Club, Costco, and BJ's spend among consumers active in the applicable window. No confidence intervals or p-values were computed. Seasonality, regression to the mean, wellness motivation, residual baseline imbalance, and changes in the consumers active after the start can affect the comparisons, so the dollar difference-in-differences is more defensible than the wallet-share result and neither establishes causality.