Unit Economics Without Jargon: CAC, Lifetime Value and Payback

Choosing the unit

Unit economics starts with a choice of unit. For a subscription app the unit is usually one customer or one account. For a delivery service it might be one order, and for a marketplace one transaction. The question is always the same: on a single unit, does the business come out ahead?

Looking at one unit strips away the noise of rapid growth. A company can report rising total revenue while losing money on every sale, as long as it keeps raising money to cover the gap. Unit economics asks what happens to each sale on its own terms.

The choice of unit is not neutral. A delivery company that measures per order may look healthy while losing money on each customer once refunds, support and marketing are counted, so it is worth checking that the unit matches the way the business actually earns and spends.

Customer acquisition cost

Customer acquisition cost, usually shortened to CAC, is what the company spends to win one new customer. In its simplest form it is total sales and marketing spending over a period divided by the number of new customers in the same period. Advertising, sales salaries, sign-up discounts and referral rewards can all belong in that figure.

The simple version can mislead. Some companies quote CAC only for paid advertising and leave out the sales team, which makes the number look smaller. Others average together customers who arrived on their own through word of mouth with those who were expensive to win, hiding the cost of growth through paid channels. Asking what is included is usually the first useful question.

CAC also tends to rise over time. The first customers are often the easiest to reach; later ones require more advertising, more persuasion or entry into markets where the product is less known.

Gross margin: what is left from each sale

Gross margin is the share of revenue left after the direct costs of delivering the product, such as hosting for software, ingredients and packaging for a meal kit, or payment processing and support for a marketplace. A business with a high gross margin keeps most of each sale; one with a low margin keeps a small slice.

Gross margin matters for unit economics because it is the money from each customer that can repay acquisition cost and eventually cover salaries, offices and everything else. Two companies with the same revenue per customer can have very different economics if one keeps most of it and the other keeps little.

Lifetime value and the ratio to CAC

Lifetime value, or LTV, is an estimate of the gross profit a customer will bring over the whole relationship. A common rough method multiplies the monthly gross profit per customer by the expected number of months a customer stays, which in turn is estimated from churn.

Founders often compare LTV with CAC. If a customer is expected to bring several times more gross profit than it cost to acquire them, the business appears to have room to grow by spending on acquisition. If the two figures are close, each new customer adds little.

The weakness of LTV is that it is a forecast. It depends on how long customers will stay, which a young company cannot yet know from experience. Small changes in assumed churn produce large changes in LTV, so the figure should be read as an estimate with wide uncertainty.

Payback period: how long until a customer pays for themselves

The payback period is the time it takes for the gross profit from a customer to cover what it cost to acquire them. In the illustrative example above, a customer bringing in a modest monthly gross profit against a larger acquisition cost takes many months to repay that cost.

Payback is popular because it relies less on long-range guesses than LTV. It also connects unit economics to cash: until payback, the company has spent money it has not yet earned back, and fast growth with a long payback period can consume a great deal of cash. That link is the subject of the next article in this series, on burn rate and runway.

Why every figure deserves a second look

Unit economics are useful because they reduce a complicated business to a few comparable figures, and that same simplicity is their limit. Each figure rests on choices about what to include, which period to measure and how to treat different groups of customers.

Averages can conceal a great deal. A business may earn healthy returns on customers from one channel and lose money on another, and the blended figure may look acceptable. Splitting the numbers by channel, region or customer type often reveals more than the headline.

Finally, unit economics describe the past or estimate the future under current conditions. Prices, competition and costs change. This article is general education and does not assess any particular business or investment.