Customer lifetime value is the gross profit a customer brings you for as long as they stay a customer. Profit, not revenue, and only for a period you can trust. It matters because it tells you how much you can spend to win one: a simple rule is to spend no more than a third of it.

The formula is short. Take what a customer pays you in a period, subtract the direct cost of serving them, and multiply by how many periods they are likely to stay. Most explanations then show a coffee shop or an online store. Below are three small-business cases instead, a one-time job, a monthly retainer and a yearly contract, with every step of the arithmetic.

The formula, in words

Lifetime value equals gross profit per period times the expected number of periods. "Gross profit" means the money left after the costs that exist only because of this customer: materials, labor, travel, payment fees. It leaves out rent and your own overhead. "Expected periods" is how long you can honestly expect them to stay, and the safe way to count is to cap it at three years.

Example 1: a one-time $200 job

Quill Mobile Detailing cleans cars for $200 a visit. After supplies, fuel and the technician's time, 55 percent is left, so $110 of gross profit per job. Not everyone comes back. Out of 100 first-time customers over three years, 35 book a second job and 15 book a third. That is 150 jobs for 100 customers, or 1.5 jobs per customer.

Revenue per customer is 1.5 times $200, or $300. Gross profit is 1.5 times $110, or $165. That $165 is the lifetime value. Notice how far it is from the $200 on the invoice: the first job alone only earns $110, and the repeat business adds $55.

Example 2: a $150-a-month retainer

Greenmark Lawn Care sells a monthly plan at $150. Direct costs run 35 percent, so $97.50 of gross profit a month. Suppose 5 percent of customers cancel each month. A rough rule: average stay equals one divided by the monthly cancel rate, so 1 divided by 0.05 is 20 months.

Revenue over 20 months is $3,000. Gross profit is 20 times $97.50, or $1,950. That is the lifetime value. If the cancel rate were 8 percent, the average stay would be about 12.5 months and the value about $1,219. So the cancel rate matters as much as the price.

Example 3: a yearly contract

Tallis IT Support sells a $3,600 annual contract with a 40 percent margin, so $1,440 of gross profit a year. Eighty percent of customers renew each year. Counting only three years: year one is certain (1.0), year two is 0.8 of customers, year three is 0.8 times 0.8, or 0.64. The expected number of years is 1.0 plus 0.8 plus 0.64, which is 2.44.

Lifetime value is 2.44 times $1,440, or about $3,514. If you counted without the three-year cap, the expected stay would be 5 years and the value $7,200. The cap keeps you honest, because five years is a long time to trust anything about a small business.

Turning value into a spend limit

The one-line rule: spend no more than a third of a customer's lifetime gross profit to win them. A third leaves two thirds for your overhead and your own pay. For the three examples that is about $55 for the detailer, $650 for the lawn plan and $1,171 for the IT contract. Those are ceilings for what it should cost you to get one customer, counting ads, tools, data and the time you spend, which your customer acquisition cost measures.

You can also work backward. If one lawn plan is worth $1,950 and you can spend $650 to win it, the question becomes how many leads that takes. Our piece on how many leads you need to get a customer turns this into a count, and what a lead costs for a small business gives the other side. For a bought-lead check on the same logic, see are buying leads worth it. And if you work backward from income instead, how many customers you need to replace your salary uses the same figures.

Work out your own number in ten minutes

You don't need software. Open your invoices or your bank deposits and take the customers who first bought from you three years ago, or the earliest group you have. Count them. Count how many are still buying, or how many bought again. That gives you your repeat rate or your stay rate, the one input you can't guess. Then pick a typical job or month, subtract what it cost to deliver (materials, labor, travel, fees), and keep the result as gross profit. Multiply gross profit by the average number of jobs or months per customer in that group. If your group is under 30 customers, treat the answer as a range, not a figure, and round down. Write the result and the date on a card by your desk and recheck it in a year.

Mistakes in the math

Using revenue instead of gross profit makes every number look about twice as good. Using the best customer's stay as the average does the same. Counting years nobody can promise inflates annual contracts. Mixing very different customers into one average hides that your biggest accounts carry the rest. Ignoring the cost of support or callbacks overstates the margin. And never updating it: renewal and cancel rates change when you change price or service, so recalculate each year. If you raise prices, how to raise prices without losing customers shows how the value moves.

Four terms that sit next to lifetime value

Customer acquisition cost (CAC) is what you spend to win a customer. Churn or cancel rate is the share who leave in a period. Retention is its opposite. Payback period is how long a customer takes to earn back what you spent to win them. Average revenue per customer is the revenue side of the formula.

Take the lawn plan again. If a month of outreach produces one new customer, worth $1,950 in gross profit, then a $24.99 monthly plan is about 1.3 percent of that value. Rocketship finds the buyers, emails them from your own Gmail, follows up, and books the meeting on its own. Plans that get you customers start at $24.99 a month (Launch), and every monthly plan starts with a 7-day free trial, card required. See the AI workers.