Payback Period Budgeting
The gate before every channel decision: can I afford this channel? Advertising has to be deterministic — $1 in, more than $1 out, on a clock you can name. Payback Period is how you set the clock.
Kill LTV:CAC first
LTV:CAC is a useless, often destructive metric. It feels rigorous and is usually a lie. Four flaws:
- It assumes all customers churn. LTV bakes in an eventual death for every account. Your best customers don't churn — they compound. A metric that pre-writes everyone's obituary underprices your actual base.
- It assumes churn is evenly timed. It isn't. Baremetrics data shows more churn happens in the first 3 months than in any other window — front-loaded, not smooth. Blended LTV smears that spike into a flat average and hides the real risk (and the real payback math).
- It hides per-plan variance under blended ARPU. A $9/mo plan and a $999/mo plan get averaged into one number that describes neither. The channels, creative, and payback that work for the $9 buyer are nothing like the $999 buyer — but blended LTV:CAC says "3:1, we're fine" and you scale the wrong thing.
- It ignores revenue delay. Free trials, free plans, and long sales cycles mean money arrives weeks or months after CAC is spent. LTV:CAC treats acquisition and revenue as simultaneous. They're not. The gap is where startups run out of cash.
A "healthy" 3:1 LTV:CAC can sit on top of a channel that bankrupts you, because the ratio never asks when the cash comes back.
The replacement: Payback Period
Payback Period = CAC / ARPU (monthly).
The answer is in months — how long until a customer pays back what you spent to acquire them. Target 3–12 months. Under 3 is often leaving growth on the table; over 12 means you're financing customers longer than most early-stage balance sheets can survive.
Because it's per-cohort and per-plan (not blended), it exposes exactly what LTV:CAC hides.
Worked example — same CAC, wildly different payback
Say a channel costs $300 to acquire a customer (CAC = $300):
| Plan | ARPU (monthly) | Payback = CAC / ARPU | Verdict |
|---|---|---|---|
| Starter | $9 | 300 / 9 = 33.3 months | Unaffordable. You wait ~3 years to break even on acquisition — before churn. Do not run this channel for this plan. |
| Pro | $99 | 300 / 99 = 3.0 months | Healthy. Bottom of the target band. Scale it. |
| Enterprise | $999 | 300 / 999 = 0.3 months | Excellent. Pays back in ~9 days. Pour budget in. |
Same CAC, same channel. On the $9 plan the channel is a cash incinerator; on the $999 plan it's a printing press. Blended LTV:CAC would have averaged these into one meaningless "we're fine." Payback Period forces you to run the channel only for the plans it can actually afford.
The practical move: compute payback per plan (or per cohort), then only turn on paid acquisition for the segments where it lands inside 3–12 months. Route the cheap-plan buyers to organic/product-led motions instead.
Discounted Payback Period (churn-adjusted)
Raw payback assumes everyone survives to pay you back. They don't — especially in those first 3 months. Adjust for it:
Discounted Payback Period = CAC / (ARPU × annual retention)
Multiply ARPU by the fraction of customers still paying, so the denominator reflects real, retained revenue instead of theoretical revenue.
Example: CAC $300, ARPU $99, annual retention 70%:
- Raw: 300 / 99 = 3.0 months
- Discounted: 300 / (99 × 0.70) = 300 / 69.3 = 4.3 months
Still inside the band — but the discounted number is the one to budget against. When retention is weak, discounted payback blows past 12 months even when raw payback looked fine; that gap is your early warning.
Using it as the channel gate
- Compute CAC for the channel (all-in: spend / customers, including creative and management).
- Compute discounted payback per plan/cohort.
- Turn the channel on only where discounted payback ≤ 12 months (aim for 3–12).
- Re-run monthly — CAC drifts up as you scale; the gate moves with it.
This composes with breakeven CPL/CPC math in b2b-paid-playbook.md: breakeven tells you the most you can pay per lead; payback tells you how long your cash is tied up — you need both to scale without running dry.
Two adjacent rules
OOH without social amplification is a waste of money. Out-of-home (billboards, transit, print) has no click, no pixel, no deterministic loop on its own. It only pays back when it's engineered to be photographed, posted, and amplified on social — the OOH buys the moment, social buys the reach. Running OOH with no social plan is buying awareness you can't measure or compound.
Narrative momentum (ad copy): the strongest-performing ads carry a story forward rather than restate a pitch — each line earns the next, building tension toward the CTA instead of front-loading features. Pair it with the discipline of testing one variable at a time (copy, then creative, then audience) so you can tell what actually moved payback. Depth on both lives in the ad-creative skill; this file only flags them as levers that change your CAC.
Source: Corey Haines, Founding Marketing, ch. 7 ("Spend budget where customers spend their time"). Payback targets and the Baremetrics first-3-months churn finding are practitioner-reported — recalibrate against your own cohort data. For attribution of the CAC inputs, see the attribution skill; for setting ARPU and plan structure, see the pricing skill.