The SaaS Metrics That Actually Matter
MRR, ARR, churn, NRR, LTV, CAC — definitions, how they connect, and which ones to track when
SaaS businesses generate a lot of data. The mistake most early-stage founders make is tracking the wrong numbers — vanity metrics that feel good but do not predict business health — or calculating the right metrics incorrectly, which is worse. This lesson maps the core SaaS metric landscape and explains what each number actually tells you.
The core metric stack
- MRR (Monthly Recurring Revenue) — The monthly revenue from active subscriptions. The most fundamental SaaS metric — everything else is built on top of it.
- ARR (Annual Recurring Revenue) — MRR × 12. Used for annual contracts and as a convenient scale indicator. "We're at $2M ARR" is the standard way to describe SaaS scale.
- Churn — Revenue or customers lost in a period. The number that quietly kills SaaS businesses. Low growth + low churn = a durable business. High growth + high churn = a leaky bucket.
- NRR (Net Revenue Retention) — The revenue retained and expanded from existing customers over time. The metric that determines whether your existing customer base grows on its own.
- LTV (Lifetime Value) — The total revenue you expect from a customer over their entire relationship with you. Determines how much you can spend to acquire them.
- CAC (Customer Acquisition Cost) — The fully-loaded cost to acquire one new customer — advertising, sales salaries, tools, and time.
How the metrics connect
These metrics form a system. MRR flows into ARR. Churn reduces MRR. NRR determines whether MRR grows from existing customers. LTV is derived from MRR per customer and churn rate. CAC must be less than LTV for the business to be economically viable. A problem in any one metric cascades through the others.
The metric relationships
MRR = sum of all monthly subscription revenue ARR = MRR × 12 Monthly churn rate = churned MRR ÷ MRR at start of month NRR = (MRR_start + expansion - contraction - churn) ÷ MRR_start × 100 Average revenue per account (ARPA) = MRR ÷ number of paying customers Average customer lifetime = 1 ÷ monthly churn rate (in months) LTV = ARPA × average customer lifetime Or: LTV = ARPA ÷ monthly churn rate LTV:CAC ratio = LTV ÷ CAC > 3:1 is the minimum viable benchmark > 5:1 is healthy
Which metrics to track at each stage
- Pre-revenue / early stage (0–$10k MRR) — Track: number of paying customers, MRR, and monthly churn. Do not yet worry about LTV/CAC — you don't have enough data for reliable calculations.
- Growth stage ($10k–$100k MRR) — Add: NRR, CAC by channel, payback period. Identify your best acquisition channel and double down.
- Scale stage ($100k+ MRR) — Add: cohort analysis, expansion MRR, Rule of 40, segment-level metrics. By this stage, the aggregate numbers are less useful than understanding what drives them.
SaaS metrics are the vital signs of your business
A doctor does not just measure one vital sign — they measure heart rate, blood pressure, temperature, and oxygen saturation together, because health is a system. MRR is your heart rate. Churn is your blood pressure. NRR tells you whether the body is getting stronger. A business that looks healthy on one metric can be critically ill on another.
Calculate metrics the same way every month
The exact formula matters less than consistency. If you change how you calculate MRR (e.g., whether you include one-time fees), your historical data becomes incomparable. Pick a method, document it, and never change it without documenting the methodology change.
Try this
List your current paying customers and their monthly subscription amounts. Calculate your MRR. If any customers churned last month, calculate your monthly churn rate. If any customers upgraded, note that as expansion MRR. These three numbers — new MRR, churned MRR, and expansion MRR — are the foundation of everything that follows in this course.