Repeat Purchase Cohort Economics

A repeat-purchase cohort groups customers by a shared starting event, usually their first order, and follows their later purchases. The denominator should remain the original group when measuring how much contribution an acquired customer ultimately produces. Counting only the people who returned makes repeat buying look more valuable than it is across everyone the business paid to acquire. Keep cohort age consistent when comparing different starting months.

Follow one cohort through two windows

Imagine 100 new customers each place an initial order contributing $25 before acquisition costs. Initial contribution is $2,500. During the next 60 days, 30 of those customers place one additional order contributing $20 each, adding $600. Total observed order contribution is $3,100, or $31 per original customer. The repeat-order contribution is $6 per original customer, although it is $20 per customer who actually returned.

Include retention and acquisition costs

If the cohort required $2,800 to acquire and $150 of follow-up marketing, contribution after those activities is $3,100 minus $2,800 minus $150, or $150. On the first orders alone, the cohort was short $300 after acquisition. Later orders recovered that shortfall in this scenario, but only after time passed. The final $150 remains available for fixed overhead; it is not a complete net profit calculation.

Do not extrapolate every repeat buyer indefinitely

A 30% observed repeat-customer rate does not imply that every customer will order 0.3 times in every future period. Some customers buy several times, some never return, and purchase intervals vary by product. Extend the table one observation period at a time with order counts, net revenue, contribution, and retention expense. If forecasting beyond observed data, label each assumed period and separate forecast totals from amounts already earned.

Compare cohorts fairly

A cohort acquired three months ago has had more opportunities to repeat than one acquired last week. Compare both at the same age, such as 60 days after first purchase. Also segment when initial product mix, promotional offer, channel, or return policy differs materially. A larger initial discount can increase customer count while reducing contribution and attracting buyers who do not return. These are possibilities to examine with records, not conclusions to assume from a single ratio.

Maintain a reproducible customer definition

Deduplicate identities, decide how canceled first purchases affect membership, and connect later refunds to the relevant orders. Record whether contribution includes original delivery, fees, returns, and any customer support costs. With no original customers, per-customer results are undefined. Negative cohort contribution is a meaningful outcome and should remain visible. The model can show whether observed purchases recovered acquisition costs; it cannot establish that future orders or marketing interventions will repeat the same pattern.

Method references: Shopify: customers reports; OpenStax: break-even and contribution analysis. Accessed October 22, 2026. All dollar figures are hypothetical worked examples.