How do I calculate customer lifetime value?

A simple version: LTV equals average revenue per customer per period, multiplied by the gross margin, divided by the churn rate. If a customer pays 100 a month at 80 percent margin and 5 percent monthly churn, LTV is roughly 100 times 0.8 divided by 0.05, which is 1,600. Use gross profit, not revenue, so the number reflects real economics.

Unit Economics: The LTV-to-CAC Math That Decides If You Have a Business

Q: What are unit economics?

Unit economics are the revenues and costs associated with a single unit of your business, usually one customer. The core question is whether one customer generates more profit over their lifetime than it costs to acquire and serve them. If yes, growth compounds. If no, every new customer loses money and scaling accelerates failure.

Q: What is a good LTV to CAC ratio?

A widely used benchmark, popularised in SaaS, is an LTV to CAC ratio of about 3 to 1. Below 1 to 1 you lose money on every customer. Around 1 to 1 you barely break even. Much higher than 5 to 1 can mean you are underinvesting in growth and could afford to acquire faster. The ratio is a guide, not a law.

Q: What is CAC payback period?

CAC payback is how many months of gross profit from a customer it takes to recover the cost of acquiring them. It equals CAC divided by monthly gross profit per customer. A common target is under 12 months. Shorter payback means cash returns faster, which reduces how much funding you need to grow.

If you lose money on every customer, you cannot make it up in volume. You just lose money faster.

Here is the trap that kills well-funded startups. Growth is up and to the right, the deck looks incredible, everyone is celebrating, and the company is quietly bleeding to death because every new customer costs more to acquire than they will ever pay back. That is not a growth story. That is a faster path to zero.

Unit economics is the antidote. It zooms all the way in to a single customer and asks one question: does this one unit make money? If the answer is yes, scaling is pouring fuel on a fire. If the answer is no, scaling is pouring fuel on yourself.

Profit per customer is the truth. Everything above it is a story.

The four numbers you must know

1. CAC: Customer Acquisition Cost

Total sales and marketing spend in a period, divided by the number of new customers it won. Spend 10,000, win 20 customers, CAC is 500. Include everything: ad spend, salaries, tools. The honest number is always higher than the flattering one.

2. Gross margin per customer

Revenue from a customer minus the direct cost to serve them. This is the money you actually keep, not the top-line price. Everything downstream uses gross profit, not revenue, or the math lies to you.

3. LTV: Lifetime Value

How much gross profit one customer delivers over their entire relationship. A simple version: monthly revenue times gross margin, divided by monthly churn. 100 a month at 80 percent margin and 5 percent churn gives roughly 1,600 in LTV. Notice churn is in the denominator, so retention is the master lever.

4. The LTV to CAC ratio

Divide LTV by CAC. In our example, 1,600 divided by 500 is 3.2 to 1. The widely cited SaaS benchmark is around 3 to 1: each customer returns about three times what they cost to win. Below 1 to 1 you are paying to lose customers. Far above 5 to 1 often means you are too cautious and could grow faster.

3:1healthy LTV to CAC benchmark

<12 motarget CAC payback

5%more retention can lift profit 25–95%

The LTV:CAC test · is it a business?

1:1 · you pay to growDead

3:1 · healthyGo

5:1 · underinvestingSpend

Lifetime value divided by acquisition cost. Below 3:1 the model leaks; 3:1 is the common healthy benchmark; far above it you are likely under-investing in growth. Pair it with CAC payback under twelve months.

Retention is the cheat code

Because churn sits in the denominator of LTV, small improvements in retention produce outsized gains. Fred Reichheld's research at Bain found that increasing customer retention by just 5 percent can raise profits by 25 to 95 percent. There is also a well-known finding that acquiring a new customer can cost several times more than keeping an existing one. So before you spend another dollar lowering CAC, ask whether you can raise LTV by keeping customers longer. It is usually the cheaper, more durable win.

CAC payback: the cash-flow view

The ratio tells you if the model is profitable. CAC payback tells you how fast the cash comes back. It is CAC divided by monthly gross profit per customer. If CAC is 500 and you earn 80 a month per customer, payback is just over six months. Under twelve months is a common healthy target. Shorter payback means you recycle cash faster and need less funding to grow, which ties straight back to Day 6.

Why founders fool themselves here

Three common lies. Using revenue instead of gross profit, which inflates LTV. Undercounting CAC by leaving out salaries and tools. And measuring blended CAC across all channels, which hides the fact that one channel is profitable and the rest are torching money. Break the numbers down by channel and cohort. The averages are comforting and the details are where the business actually lives.

The takeaway

Know your CAC, gross margin, LTV and LTV to CAC ratio before you scale anything.
Aim for roughly 3 to 1 LTV to CAC and CAC payback under twelve months.
Use gross profit, not revenue, and count every cost in CAC. Honest numbers only.
Retention is the highest-leverage lever. A 5 percent lift can move profit 25 to 95 percent.

Frequently asked questions

What are unit economics?

The revenues and costs tied to a single unit, usually one customer. The question is whether one customer earns more over their lifetime than it costs to acquire and serve them. If yes, growth compounds. If no, scaling accelerates failure.

What is a good LTV to CAC ratio?

About 3 to 1 is the common benchmark. Below 1 to 1 you lose money per customer. Far above 5 to 1 can mean you are underinvesting in growth. Treat it as a guide, not a law.

How do I calculate lifetime value?

A simple version: monthly revenue times gross margin, divided by monthly churn. 100 a month at 80 percent margin and 5 percent churn is about 1,600. Always use gross profit, not revenue.

What is CAC payback period?

How many months of gross profit it takes to recover the cost of acquiring a customer. CAC divided by monthly gross profit per customer. A common target is under twelve months.

"When growth comes easy" is a warning sign.

Kill My Startup shows why healthy-looking growth on broken unit economics is one of the quiet signals founders mistake for good news.

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Sources

Reichheld, F. research at Bain & Company on retention and profitability.
David Skok, "SaaS Metrics 2.0," LTV to CAC and CAC payback benchmarks.
Standard customer-acquisition cost studies on the cost of acquisition versus retention.