The LTV:CAC ratio is the single number that tells you whether your brand is a business or a money-laundering operation for venture capital. It compares what a customer is worth over their lifetime (LTV) to what it cost to acquire them (CAC). Get it right and you know whether to pour fuel on the fire. Get it wrong — and most brands get it wrong in the same predictable way — and you’ll scale yourself straight into a cash crisis.
This is a deep dive within the broader e-commerce analytics guide. Here we’ll get the number right.
The formula (the easy part)
LTV:CAC = Customer Lifetime Value ÷ Customer Acquisition Cost
- CAC = total acquisition spend ÷ new customers acquired, for the same period. Include ad spend, agency fees, and the tools that exist only to acquire. Not your rent.
- LTV = the value a customer generates over their relationship with you.
The formula is trivial. The reason teams get it wrong is entirely in how they define LTV.
The mistake that sinks brands: revenue LTV
Here is the error I see in nearly every brand I audit: they calculate LTV on revenue instead of contribution margin.
If a customer spends $300 with you over two years, that is not $300 of value. Subtract:
- COGS (what the product cost you)
- Shipping and fulfillment
- Payment processing
- Returns
A brand with 40% gross margins that thinks its $300-revenue customer is worth $300 is overstating real value by 2.5x. They then “discover” they can afford a $100 CAC at a glorious 3:1 ratio — when the true margin LTV is $120 and the real ratio is a barely-breathing 1.2:1.
Always use contribution-margin LTV. Revenue LTV is how brands feel great right up until they run out of cash.
A clean LTV estimate looks like:
LTV = AOV × Gross Margin % × Purchases per Year × Avg. Customer Lifespan (years)
You can run your inputs through the LTV Calculator to get a defensible number, and pressure-test the AOV assumption with the AOV Calculator.
What “good” actually looks like
You’ve heard the rule: 3:1 is healthy, below 1:1 you’re losing money, above 5:1 you’re under-investing in growth.
That rule is a fine starting point and a lazy stopping point. Two reasons it misleads:
- It ignores payback period. A 3:1 ratio where it takes 14 months to recoup CAC is far more dangerous for a self-funded brand than a 2:1 ratio that pays back in 2 months. Cash flow kills more DTC brands than bad ratios do. Watch CAC payback period (months to recoup acquisition cost from contribution margin) alongside the ratio — for most DTC brands you want payback under 6 months, ideally under 3.
- It hides the trend. A blended 3:1 can be a great 5:1 on your best channel propping up a catastrophic 1:1 on the channel you’re scaling. Always look at LTV:CAC by channel and by cohort, not blended.
Why retention is the real lever
Look at the LTV formula again. The two inputs you can most move are purchases per year and customer lifespan — both of which are retention. CAC has a floor (auction prices only go up). LTV has a ceiling only as high as your repeat rate.
This is why retention work usually beats acquisition optimization for improving the ratio. Before you try to lower CAC, find out whether customers come back: start with customer retention rate (CRR), then read it properly with cohort analysis, and benchmark against your category with the Repeat Purchase Scorer.
How to actually use the number
- Set an acquisition ceiling. If target payback is 3 months and 3-month contribution margin per customer is $80, your max CAC is $80. Hand that to your media buyer as a hard rule.
- Decide where the next dollar goes. Scale channels with healthy channel-level LTV:CAC; fix or cut the rest. The Channel Scorecard compares them on incremental contribution.
- Forecast cash, not vanity. Model when CAC gets repaid so you don’t outgrow your bank balance.
The bottom line
LTV:CAC is simple arithmetic wrapped around two honest inputs. Use margin, not revenue, watch payback period next to the ratio, and never trust a blended number. Do that and you’ll know — with a number you can defend to an investor or a bank — whether to scale or to fix the engine first.
If your LTV:CAC is murky because your data won’t reconcile and your CAC reads differently on every platform, that’s the e-commerce analytics work I do. Book a call and we’ll get you a number you can build on.