A subscription business doesn't live or die on a single month's revenue — it lives on whether that revenue recurs, grows, and outruns the cost of winning it. Five metrics tell that story: MRR and ARR, churn, CAC, CAC payback period, and the LTV:CAC ratio. Here's what each one means and how they fit together.
MRR and ARR: the foundation
Monthly recurring revenue is your paying customers multiplied by the average revenue each pays per month (ARPU). Annual recurring revenue is simply MRR × 12. If you have 200 customers paying $50/month, that's $10,000 MRR and $120,000 ARR. The reason SaaS founders obsess over MRR rather than total revenue is that it strips out one-off fees and shows the predictable, repeatable core of the business. The MRR & ARR calculator also projects where ARR lands after a year at your current growth rate — a quick reality check on any plan.
Churn: the silent killer
Churn rate is the percentage of customers (or revenue) you lose in a period. Lose 25 of 500 customers in a month and that's 5% monthly churn — and 95% retention. It sounds small, but it compounds against you: at 5% monthly churn, the average customer stays only about 20 months (roughly 1 ÷ churn). High churn means you're refilling a leaky bucket — every new sale first has to replace a lost one before you grow. Check yours with the churn rate calculator, and treat retention as a growth lever, not an afterthought.
CAC: what a customer costs to win
Customer acquisition cost is total sales and marketing spend divided by the new customers it produced. Spend $6,000 to land 50 customers and your CAC is $120. On its own the number is meaningless — $120 is cheap for an enterprise account and ruinous for a $5/month app. It only has meaning next to two things: how fast you earn it back, and how much the customer is ultimately worth. The CAC calculator works it out and, if you add lifetime value, shows your LTV:CAC ratio in one step.
CAC payback period: how fast you earn it back
This is the metric that separates businesses that can grow on their own cash from those that constantly need to raise more. CAC payback period is how many months of gross profit it takes to recoup the cost of acquiring a customer: CAC ÷ (monthly revenue × gross margin). A $300 CAC against $50/month at 80% margin earns back in 7.5 months. Shorter payback frees up cash to reinvest sooner; many SaaS companies aim for under 12 months, and under 6 is excellent. The CAC payback period calculator turns your numbers into a month count instantly.
LTV:CAC: the payoff ratio
Finally, lifetime value — the total profit a customer brings over the whole relationship — sets the ceiling on what you can afford to spend acquiring one. The benchmark that ties everything together is the LTV:CAC ratio, and a widely used target is 3:1: three dollars of lifetime value for every dollar of acquisition cost. Below 1:1 you lose money on every customer; far above 3:1 can mean you're under-investing and leaving growth on the table. Estimate it with the customer lifetime value calculator.
How they fit together
Read them as a system. MRR/ARR measures the size of the recurring base; churn measures whether it leaks; CAC measures what growth costs; payback period measures how fast that cost returns as cash; and LTV:CAC measures whether the whole loop is profitable over time. A business can post record revenue and still be unhealthy if churn is high and payback is long — and a smaller one with low churn and fast payback can compound past it. Run your own numbers through the calculators above before you decide to pour fuel on the fire.