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:

1. 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.
2. 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).
3. 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.
4. 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

Revenue-only ratio = CAC / monthly ARPU. For acquisition-cost recovery use gross-margin payback = CAC / (monthly ARPU × gross margin), with gross margin as a fraction. The revenue-only ratio assumes 100% gross margin; it excludes serving costs. See the CAC payback definition.

The simplified ratio is in months and assumes steady monthly gross profit with no churn or collection delay. A 3–12 month target is a planning reference. Choose a target using your cash runway, margins and cohort recovery; a shorter or longer ratio alone does not justify changing spend.

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). The table below is revenue-only, before serving costs and churn; it is a comparison, not permission to scale:

Same CAC does not imply the same affordability. At 20% gross margin the $99 plan takes 300 / (99 × 0.20) = 15.2 months even before churn, despite its 3.0-month revenue-only ratio. Compare plans separately and verify serving costs before approving spend.

The practical move: compute recovery per plan (or per cohort) against measured margin, retention and cash timing. Use the 3–12 month target as a planning assumption to compare with runway, not a universal approval rule.

Cohort recovery — account for when churn happens

CAC / (ARPU × annual retention) is not discounted payback. A single year-end retention percentage cannot identify the monthly recovery path. Time-value discounting requires an explicit discount rate; retention describes customer survival.

For a cohort, find the first month where cumulative gross profit per original acquired customer covers CAC:

Cumulative recovery through month n = sum(ARPU_t × gross_margin_t × retained_fraction_t)

Use measured retained revenue per original customer instead when available; do not multiply by retention again. Include collection delay when assessing cash recovery. If the observed cohort has not recovered CAC, report that rather than inventing a payback date.

Example: CAC $300, ARPU $99 and 80% gross margin. Two cohorts both retain 70% at month 12:

• Early loss: 70% retained in every month 1–12 → $55.44 monthly gross profit per original customer; recovery first crosses $300 in month 6.
• Late loss: 100% retained in months 1–11, 70% at month 12 → $79.20 for the first eleven months; recovery crosses $300 in month 4.

The old single-retention ratio gives the same 4.3 months to both cohorts and ignores gross margin. Their actual recovery differs despite identical year-end retention.

Using it as the channel gate

1. Compute CAC for the channel (all-in: spend / customers, including creative and management).
2. Compute gross-margin payback and check the measured cohort recovery path, including revenue collection timing.
3. Compare recovery with runway and your chosen target (the 3–12 month band is a planning reference). Do not scale on a revenue-only ratio or annual retention multiplier.
4. 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.*