Unit Economics CAC:LTV Payback Analyzer

Formula

LTV = (ARPU × Margin%) / Churn%

Lifetime Value (LTV) represents the total gross profit expected from a single customer. It is calculated by taking monthly profit (ARPU * Margin) and dividing by the monthly churn rate. The Payback Period is simply CAC divided by Monthly Profit.

Worked Examples

Example 1: SaaS Startup

Problem:CAC $250, ARPU $50, Margin 80%, Churn 3%.

Solution:Monthly Profit: $40. LTV: $40 / 0.03 = $1,333. Ratio: 5.3x. Payback: $250 / $40 = 6.25 months.

Result:Healthy (5.3x LTV:CAC)

Frequently Asked Questions

What is a 'good' LTV:CAC ratio?

3:1 is the industry standard benchmark for SaaS. 4:1 or 5:1 is excellent. Below 1:1, you are losing money. Between 1:1 and 3:1, you are likely burning cash too fast.

How do I calculate CAC?

Total Sales & Marketing Expense (Ad spend + Salaries + Commissions + Tools) divided by the Number of New Customers Acquired in that period.

Should I include organic leads in CAC?

For 'Blended CAC', yes. For 'Paid CAC', no. Blended CAC tells you overall business health; Paid CAC tells you if your ad channels are working.

How does Churn affect LTV?

It is the denominator. Halving your churn doubles your LTV. It is the most sensitive variable in the equation.

What is Payback Period?

The time it takes for a customer's profit payments to pay off the cost of acquiring them. Shorter is better for cash flow.

Can LTV be infinite?

Theoretically, if churn is 0%, LTV is infinite. In practice, companies die, markets change, or everyone churns eventually. We usually cap LTV periods at 3-5 years for realism.

How do I fix bad unit economics?

Raise prices (increases LTV and lowers Payback), fix churn (increases LTV), or optimize marketing channels (lowers CAC).

How do significant figures affect unit conversions?

Your converted result should have the same number of significant figures as your original measurement. If you measure 5.2 inches (2 significant figures), converting to centimeters gives 13 cm, not 13.208 cm. Using excessive decimal places implies false precision.

When should I use metric vs imperial units?

Use metric for science, medicine, international communication, and precision work. Use imperial when required by local convention (US construction, cooking, road signs). Engineering increasingly uses metric. Always match the unit system expected by your audience or industry.

What are the most common unit conversion mistakes?

Common errors include confusing fluid ounces with weight ounces, mixing up miles and nautical miles, forgetting that UK and US gallons differ (UK is 20% larger), using the wrong temperature formula, and not accounting for the difference between troy and avoirdupois ounces.

Background & Theory

The Unit Economics Analyzer determines if your business model works at the fundamental level of one single customer. ## Concept Overview If you sell dollar bills for 90 cents, you can grow infinitely fast but will go bankrupt. Unit economics checks if you are selling dollar bills for $1.10. * **CAC:** Cost to get a customer. * **LTV:** Value you get from them over time. * **Payback:** Time to earn back the CAC. ## Key Variables & Intuition * **Churn:** The LTV killer. A small increase in churn drastically reduces LTV. * **Gross Margin:** Often ignored. SaaS has 80% margins; E-commerce has 30%. A $100 SaaS sub is worth far more than a $100 E-com order. * **ARPU:** Expansion revenue (upsells) can offset churn, leading to "Negative Churn" (growing value). ## Assumptions * Churn is constant (exponential decay of cohort). * CAC is paid upfront (Cash flow negative at Month 0). * Calculations uses *Gross Profit*, not Revenue (Best Practice). ## Limitations & Edge Cases * **Non-linear Churn:** Users often churn heavily in Month 1 and then stabilize. A flat rate might underestimate LTV. * **Viral Growth:** High K-factor (referrals) effectively lowers CAC, which isn't captured in simple direct CAC math. * **Discounting:** Future cash flows should be discounted (NPV), especially for long LTVs (5+ years). This calculator uses nominal LTV. ## Practical Tips * **Segment your CAC:** Blended CAC hides the truth. Calculate LTV:CAC for "Paid Ads" vs "Organic" separately. * **Focus on Payback:** In a recession, optimize for <12 month payback to preserve runway. * **Include Retention:** Improving retention by 10% often moves the needle more than lowering CAC by 10%. ## Common Mistakes * Calculating LTV on Revenue instead of Gross Profit. * Dividing Total Marketing Spend by *New* Customers (correct) vs dividing by *Total* Customers (wrong). * Ignoring the "Cost of Service" (Support, Hosting) in the Gross Margin.

History

Unit Economics analysis has transitioned from obscure accounting metrics to the primary heartbeat of the startup ecosystem. ## Origins & Why It Emerged Before the SaaS boom, businesses sold perpetual licenses. "Sales" were one-time events. The shift to subscription models (recurring revenue) broke traditional accounting. A "sale" now cost money upfront (CAC) but paid back over time. Investors needed a way to value these future cash flows. ## How It Evolved in Practice In the early 2010s, VCs like David Skok popularised the "SaaS Metrics 2.0" framework. LTV:CAC became the golden ratio. Startups began to run "unprofitable" P&Ls that were actually highly profitable on a unit basis. This justified the massive valuations of companies like Salesforce and HubSpot. ## Modern Usage Today Today, "Unit Economics" applies to everything, not just SaaS. Uber (Ride LTV), DoorDash (Order LTV), and D2C brands all live by these metrics. The focus has shifted from "Growth at all costs" (2020) to "Profitable Unit Economics" (2023+). "Payback Period" has overtaken LTV:CAC as the most critical metric due to higher interest rates (cost of capital). ## Common Misconceptions * **"LTV is revenue":** No, LTV is *Gross Profit*. Revenue doesn't pay the rent; margin does. * **"CAC is just ads":** CAC includes sales commissions, salaries, and tooling. Fully Loaded CAC is the real number. * **"3:1 is a law":** It's a guideline. 3:1 with a 24-month payback is worse than 2:1 with a 1-month payback in a cash-constrained environment.