Retention rate is the percentage of customers or users a company retains over a defined period, typically measured monthly (MRR) or annually. It's calculated by dividing the number of customers at the end of a period minus new customers acquired, by the number of customers at the start of the period. For subscription and SaaS businesses especially, retention rate is one of the most predictive metrics of long-term success and profitability.
How It Works
Most startups track retention using a cohort analysis approach. A cohort is a group of customers who signed up during the same period. You then measure what percentage of that cohort remains active after 30 days, 90 days, or 12 months. A company with 90% monthly retention keeps nine of every ten customers each month. Over time, this compounds—a 90% monthly retention rate looks very different from an 80% rate over a year.
The inverse metric, churn rate, shows what percentage of customers leave. If retention is 90%, churn is 10%.
Why It Matters for Investors
Retention is arguably the most honest metric about product quality and business fundamentals. You can fake growth through aggressive marketing, but you can't fake retention—it reveals whether customers actually find value in what you're selling. High retention means the company has achieved product-market fit, reducing the need for constant customer acquisition to maintain revenue.
For investors evaluating unit economics, retention directly impacts customer lifetime value (LTV). A customer retained for three years generates far more profit than one who leaves after six months, even at identical monthly prices. This makes retention a primary driver of whether a business can scale profitably.
Example
A B2B SaaS platform launches with 1,000 customers in January. By February, they've added 200 new customers but lost 150 from January's cohort. Their retention rate is (1,000 - 150) / 1,000 = 85%. In March, they retain 85% of February's base again. This predictable retention allows the company to model future revenue accurately and shows investors they're building something sticky. Compare this to a competitor with 60% monthly retention—growth becomes a race against constant attrition.
Key Takeaways
- Retention rate reveals whether customers find lasting value in a product; it's harder to fake than growth metrics.
- High retention (typically 80%+ monthly for B2B SaaS, 85%+ for B2C) is a green flag for sustainable business economics.
- Retention directly impacts customer lifetime value and profitability at scale—it's foundational to unit economics.
- Track retention by cohort to understand how different customer segments behave and identify when product changes affect loyalty.