What is customer retention?
Customer retention is the share of customers who continue to use a product or service over a defined period — the inverse of churn. In SaaS and subscription businesses retention is the primary determinant of LTV and the steepest lever on long-term value. A small improvement in monthly retention compounds dramatically over time.
Formula
Customer retention over a period:
Customer Retention Rate = (Customers at End − New Customers Added) ÷ Customers at Start
For a B2B SaaS that started the quarter with 200 customers, added 30 new and ended with 210: retention = (210 − 30) ÷ 200 = 90% (10% customer churn).
Retention vs. related metrics
- Gross retention vs. net retention: gross excludes expansion (caps at 100%); net includes upsell and can exceed 100%. Best-in-class SaaS prints NRR > 120%.
- Customer retention vs. revenue retention: a customer churning while others upgrade may show flat revenue retention but falling customer retention — a hidden risk.
- Cohort retention: tracks the same group of customers over time; the only way to see retention curves stabilising (or not).
Why retention is the highest leverage point
In a Bain study cited across the literature, a 5% increase in retention can drive a 25%+ profit improvement because retained customers have lower service cost, higher expansion likelihood and lower acquisition cost amortisation. The fastest-growing public SaaS companies are those with the best NRR — not those with the lowest CAC.
Do: build a cohort retention table at month 1, 3, 6, 12; investigate the steepest drop-offs as product or fit problems.
Don’t: mask retention problems with aggressive acquisition — the leaky bucket eventually overwhelms the spend.