CAC and LTV Calculation

1. What CAC and LTV Actually Measure

CAC is the fully loaded cost of acquiring one new customer. LTV is the gross profit that customer generates across their relationship with you.

The pairing matters because neither is useful alone. A high CAC is fine if LTV is higher still. A low CAC means nothing if customers leave in four months.

2. Why Most Calculations Are Too Generous

The usual CAC calculation divides advertising spend by new customers. That answers what advertising costs per customer, not what acquisition costs, and the gap is often the larger number.

On the LTV side, using revenue instead of gross profit inflates the figure by whatever your cost of delivery is. A business at 60% gross margin that uses revenue overstates LTV by 67%.

Unit economics saas analysis fails most often through these two errors together, which compound rather than offset.

• CAC using ad spend alone omits the largest component for most businesses
• LTV using revenue inflates the figure by the full cost of delivery
• Blended CAC hides that one channel is subsidising another
• Optimistic lifetime assumptions compound every other error in the chain

3. How to Pick the Right Period

Startup financial metrics generally need a quarter of data to mean anything. Use a quarter rather than a month for most businesses. Monthly figures on low customer volume produce noise that invites reaction rather than insight.

There is also a timing mismatch. Spend in one month acquires customers across the next two or three, so matching a month’s spend to a month’s customers misattributes both.

• Quarterly for CAC on most businesses, monthly only at high volume
• Account for lag between spend and the customer it acquired
• Segment by channel so a cheap channel is not hidden by an expensive one
• Separate new from expansion revenue when calculating LTV
• Recalculate quarterly, not continuously

4. 8 Steps to Calculate CAC and LTV Correctly

Steps one to four build CAC. Steps five to eight build LTV and the measures that follow.

Step 1: Total All Acquisition Spend

Advertising, content, events, sales tooling, and the fully loaded cost of every sales and marketing person including payroll tax and benefits. Anything spent to win customers belongs here.

Step 2: Exclude Retention Costs

Customer success, onboarding support and account management are retention spend, not acquisition. Including them inflates CAC and understates the efficiency of your acquisition engine.

Step 3: Count New Customers in the Same Period

Genuinely new logos, not upgrades or reactivations. Expansion revenue from an existing customer is not an acquisition and counting it understates CAC considerably.

Step 4: Divide and Then Segment

Total spend divided by new customers gives blended CAC. Then split by channel, because blended CAC routinely conceals one channel at 4x the cost of another.

Step 5: Calculate Average Revenue Per Customer

Monthly or annual, depending on your billing. Use the average for genuinely comparable customers rather than across an entire base with wildly different contract sizes.

Step 6: Apply Gross Margin

Multiply by gross margin to get gross profit per customer. Saas finance metrics convention is that LTV is a profit figure, not a revenue figure, and this is the single most common error in the calculation.

Step 7: Estimate Lifetime Honestly

One divided by monthly churn rate gives average lifetime in months. For young businesses this extrapolates from limited data, so cap it at three years rather than projecting a decade.

Step 8: Calculate Payback Period

CAC divided by monthly gross profit per customer. Cac and ltv calculation produces a ratio, but payback period describes cash timing, which is what actually constrains a growing business.

Startup financial metrics should include both, because a strong ratio with a long payback can still exhaust your cash.