The LTV:CAC ratio is the single number most often used to judge whether a company's growth is sustainable. Below 1:1, the business loses money on every customer it acquires, no matter how much revenue shows up on the top line. Between 1:1 and 3:1 is considered marginal — the unit economics work, but with little room for error.
3:1 to 5:1 is generally treated as the healthy range: customers generate meaningfully more value than they cost to acquire, while the business is still spending enough on growth to keep winning new customers. A ratio well above 5:1 can actually be a yellow flag rather than purely good news — it often means a company is being too conservative with growth spending.
The ratio should always be read alongside CAC payback period (how many months it takes to recover the acquisition cost), since a business can have excellent long-term unit economics and still run out of cash waiting for that payback to happen.