Dose 219: The 3:1 LTV to CAC Ratio Is a Myth (What to Measure Instead)

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Matt here with your weekly Subscription Prescription 💊

This week we're talking about money. Specifically, the number everyone quotes and almost nobody defines: the 3:1 LTV to CAC ratio.

I had a great conversation this week with Jon Blair, founder of Free to Grow CFO. He runs fractional finance for consumables brands, and when I asked him about the 3:1 benchmark, he called it a myth.

That got my attention, because I hear that number constantly. The Grüns founding team has talked openly about strict adherence to 3:1 as they scaled, and plenty of founders are chasing the same ratio.

By the end of our conversation, I agreed with Jon. The ratio isn't the problem. The way brands use it is. So let's break down what to measure instead.

1. LTV means nothing until you say margin and say when

The 3:1 number came out of the COVID ecommerce boom, when PE firms and VC funds needed a quick screen. It stuck. But it hides two questions that matter more than the ratio.

Are you talking about LTV in revenue dollars or margin dollars? And over what window?

Here's the problem. What Shopify, Lifetimely, or Triple Whale call LTV is usually average spend per customer in a cohort. That's lifetime revenue, not lifetime value. I'm guilty of blurring the two myself, and I've started correcting it.

To get to real LTV, multiply that revenue by your margin before marketing spend. Sell a $50 product with $10 landed cost, $5 shipping, and $5 pick and pack, and you're at 60% margin. A $150 revenue cohort is really a $90 margin cohort.

That $90 is what you compare to CAC. Subtract the two and you have profit per customer. Start blended across your catalog. There's a point where precision costs more than it returns.

Then the window. A 3:1 ratio on 12-month revenue would sink most brands on cash flow alone. A 3:1 on six-month margin might actually work. Same ratio, completely different businesses.

Takeaway: Stop quoting LTV without two qualifiers. Say "six-month LTV in margin dollars" or don't say it at all. The number only means something once it's bounded.

2. Your payback window is set by your capital, not a benchmark

Once the definitions are straight, the first number I'd look at isn't a ratio. It's the payback month. In what month does accumulated margin per customer equal what you paid to acquire that customer? If CAC is $50 and you hit $50 in margin by month three, that's your break-even.

For most consumables brands, three to six months is the healthy range. Where you sit inside it depends on something a benchmark can't tell you: how much cash you have.

Think of it as a seesaw. One side is the loss you take on every new customer. The other is the margin coming back from older cohorts through repeat purchases. You can only tip toward acquisition as fast as returning margin pushes it back.

A bootstrapped brand that started on $10,000 of inventory needs to break even in two or three months. Not because that's the right answer in theory, but because that's all the cash there is. Grow as fast as that allows, and no faster.

A funded brand can stretch. Jon shared one that came to him paying back CAC in 12 months, which is normally a death sentence. Investors covered two years of work to fix it. Today they pay back in four months, they're cash flow positive, and they're scaling fast.

Here's the lesson I took from that: you can't grow fast, stretch your payback period, and be tight on capital all at once. Pick two. The brands trying all three are the ones I watch run out of road.

And watch how LTV accumulates at 6, 12, and 24 months. A brand whose cohorts stop contributing after year one is a different business from one still compounding in year three.

Takeaway: Find your payback month before you touch a ratio. Then match your growth pace to the cash you actually have, and only stretch the window once older cohorts are still paying you.

3. Blended numbers hide the decisions that matter

Blended LTV to CAC is the starting point. It's not where you stop, because the first cut below it changes strategy.

Split subscribers from non-subscribers. What you'll usually find is counterintuitive. A deeper discount for subscription opt-in means a bigger loss on order one, but subscribers carry significantly higher LTV. That steeper loss gets paid for by the retention behind it.

I've seen brands scale faster and more profitably by making the subscription incentive more aggressive, not less. But that only holds if you're checking it every month. As spend climbs, Meta pushes you into a wider, looser audience, and the math that justified the discount can quietly break.

That's why I like sensitivity analysis. Ask what happens if CAC goes up 25% and LTV drops 25%. Where does break even land? You can model this in Claude in an afternoon, and it tells you how far you can push before the bet turns bad.

The next cut is by product. Which SKU drives acquisition, and which drives retention? They're often not the same. One brand Jon works with couldn't make Amazon work until the data showed a different hero product was winning new customers there. They rebuilt the Amazon opt-in around it and sales took off.

Same logic for launches. If your capsule customers are already buying protein powder from someone else, your new protein powder is a retention SKU, not an acquisition SKU. Those two outcomes need completely different math.

Takeaway: Segment blended LTV to CAC into subscribers versus non-subscribers, then into acquisition SKUs versus retention SKUs. Review the subscriber cohort monthly, because that's the segment funding your discount.

Bottom line: The 3:1 ratio isn't wrong. It's just incomplete. LTV only counts in margin dollars over a stated window, the first number that matters is payback month, and the right window depends on your cash, not someone else's benchmark. Then segment, because the subscriber cohort is where the model either holds or breaks.

One last thing that stuck with me: if you see a stockout coming, cut ad spend until it's fixed. Paying $100 to acquire a subscriber you can't ship to in month three is the most expensive mistake in this business.

Until next Tuesday, that's your Subscription Prescription. 💊

- Matt Holman 🩺