Question 1

What is CAC, and how do you calculate it?

Accepted Answer

Customer Acquisition Cost is the total sales-and-marketing spend in a period divided by the number of new customers acquired in that period. Fully-loaded CAC includes salaries of S&M staff, paid advertising, content production, sales tooling, and conference / event spend — not just paid media. Most operators understate CAC by 30–50% by counting only the ad spend. The headline rule of thumb from David Skok's SaaS Metrics 2.0: a healthy SaaS business has LTV:CAC ≥ 3 and CAC payback ≤ 12–18 months. Source: forentrepreneurs.com/saas-metrics-2.

Question 2

How is LTV calculated?

Accepted Answer

Customer Lifetime Value (gross margin-adjusted) = Average Revenue Per Customer × Gross Margin ÷ Monthly Churn Rate. The intuition: each customer pays you ARPC × Gross Margin in dollars per month, and the average customer stays 1 ÷ churn months. Multiply them together for the total margin contribution per customer over their lifetime. Caveat: this formulation assumes constant churn, no expansion revenue, and no time-discounting. The NRR-adjusted version below corrects for expansion; serious financial models also discount future cash flows back to present value, which makes LTV materially smaller than this calculator shows.

Question 3

What's a good LTV:CAC ratio?

Accepted Answer

Bessemer's 2021 State of the Cloud framework: under 3x is concerning (you're not generating enough lifetime value to justify acquisition cost), 3x–5x is healthy, and 5x+ is world-class. But there's an under-acknowledged failure mode at 5x+: it usually means you're under-investing in S&M and leaving growth on the table. Pair the ratio with the magic number — if LTV:CAC ≥ 5 AND magic number > 0.75, the answer is to spend more on S&M, not less. Source: bvp.com/atlas/state-of-the-cloud.

Question 4

What's a good CAC payback period?

Accepted Answer

The cleanest rule of thumb: under 12 months is healthy for SaaS, 12–18 months is acceptable for higher-ARPC enterprise sales (where contracts are 1–3 years anyway), and over 18 months requires exceptional retention to actually pay back. Below 6 months is world-class but rare outside of viral or highly-product-led businesses. CAC payback compounds with churn — at 5% monthly churn, an 18-month payback period means many customers churn before you've even broken even on acquiring them. Always read CAC payback alongside churn.

Question 5

What is NRR (Net Revenue Retention) and why does it matter?

Accepted Answer

Net Revenue Retention measures the change in revenue from the existing customer base over a period (typically annualized). NRR > 100% means existing customers are net-expanding (upsells, expansions, price increases > churn + downsells). Top-quartile SaaS is at 120–140% NRR; world-class is 130%+. Below 100% is a red flag — your business is leaking. NRR-adjusted LTV uses (churn − expansion) as the effective decay rate, which can make LTV materially higher (or lower) than the simple churn-based formula. When NRR is high enough that monthly net expansion exceeds churn, LTV is mathematically infinite — the cohort grows forever.

Question 6

What is the magic number?

Accepted Answer

Tomasz Tunguz's 'magic number' is (annualized net new ARR) ÷ (annualized S&M spend). It answers: for every dollar of S&M spend, how many dollars of recurring revenue do you generate? Above 0.75 = growth mode (your S&M is so productive you should be spending more); 0.5–0.75 is healthy; under 0.5 means S&M efficiency is breaking down and adding marketing dollars won't add proportional revenue. Magic number is strictly more honest than LTV:CAC for diagnosing 'should I spend more on growth?' because it doesn't depend on churn assumptions or LTV horizon. Source: tomtunguz.com/magic-number.

Question 7

When does the LTV formula break down?

Accepted Answer

Three scenarios: (1) Pre-revenue or low-revenue companies — the divisor (churn) is too small a sample, the metric explodes meaninglessly. Wait until you have 200+ customers across 6+ months. (2) Lumpy enterprise sales — churn isn't a useful month-over-month metric when you have 30 customers and one churns every quarter; use cohort retention curves instead. (3) Discount-driven growth — you can lower CAC by aggressively discounting, which inflates near-term ARPC retention but shortens future LTV. LTV:CAC should always be evaluated alongside NRR and gross margin trend lines.

Question 8

Should I be optimizing for LTV:CAC or for payback period?

Accepted Answer

Different stages care about different metrics. Early-stage / cash-constrained companies care about CAC payback because cash recovery beats long-term math when you're 9 months from running out of money. Later-stage / well-capitalized SaaS care about LTV:CAC because they can fund a longer payback period in exchange for compounding cohort revenue. Public-company benchmarks favor LTV:CAC because investors are pricing the long-term value of the customer base. The practical answer: track both, and if they diverge, go with payback when cash-constrained and LTV:CAC when growth-funded.

CAC + LTV + Payback Calculator

What this means

Worked example

Frequently asked questions

Show the math