Clients retained at 12 months

• Metric

  Current-user retention rate (CURR)

  share of current users who stay active

  Share of yesterday's current users (active that day and in the prior week) who are active again today. In Duolingo's growth model, lifting this rate moved daily actives more than any other transition.

• Metric

  Power-user curve (L28, or L7 for workweek products)

  users by days active in the month

  Histogram of monthly active users by how many days (1-28) they did the core value event. A right-leaning smile shows a daily core; successive monthly curves should shift right. Use L7 (days out of 7) for workweek products.

• Metric

  Repeat customers at months 6-12

  share of a cohort still buying in months 6 to 12

  Share of a first-order cohort that orders again in months 6 to 12 after their first purchase. The Stay health metric for stores: whether repeat buying settles into a stable base.

• Metric

  Net revenue retention (12 months)

  revenue kept and grown from existing customers

  Recurring revenue from a starting customer cohort twelve months later, including expansion, contraction and churn, divided by its starting revenue. Above 100% means existing customers grow revenue on their own.

• Metric

  Resurrection rate

  dormant users who come back

  Share of dormant users (inactive more than 30 days) who become active again in the period. Separate from reactivation after 8-30 days away. The primary win-back metric.

• Metric

  SaaS quick ratio

  revenue added per revenue lost

  New plus expansion recurring revenue divided by churned plus contracted revenue in the same period. A target of 4 is widely repeated but weakly sourced; under 1 means recurring revenue is shrinking.

Sources

Book content is paraphrased, never quoted at length. Last verified October 24, 2026.