How Long Until a Customer Pays You Back

Why this matters

Payback period answers the cash-flow question that LTV:CAC ignores: how long until we recover what we spent acquiring this customer? A company with a 3:1 LTV:CAC ratio but a 36-month payback period needs three years of uninterrupted revenue per customer just to break even on acquisition — a serious cash constraint. Founders and operators who understand payback period can make smarter decisions about how aggressively to scale without burning cash.

Demo

Payback Period (months) = CAC ÷ (Monthly Revenue per Customer × Gross Margin %). This is the number of months until the gross profit from a customer equals what was spent acquiring them.

Try it yourself

1. Change cac to 400 and observe how payback crosses 11 months — identify the point at which payback exceeds a typical annual contract length.
2. Add an expansion_mrr variable (revenue from upsells/cross-sells in months 3–6) and recalculate payback using cumulative gross profit — compare it to the simple formula.
3. Build a two-variable sensitivity table: payback period for CAC in [100, 200, 300, 400] and gross margin in [0.50, 0.65, 0.80].
4. Look up the payback period guidance from one investor (Bessemer, a16z, or Lenny Rachitsky) and note whether they use gross-profit payback or revenue payback, and why the distinction matters.

References

• https://www.lennysnewsletter.com/p/what-is-a-good-payback-period
• https://www.bvp.com/atlas/scaling-to-100m