Startup
CAC Payback Period Calculator
CAC Payback Period calculator: calculate how many months to recover your customer acquisition cost from gross profit, and check your LTV:CAC ratio health.
Result
Payback at 24.8 months is unsustainable. Pause heavy acquisition spend and fix CAC or improve ARPU/margins first.
Unit economics snapshot
CAC against the gross profit a customer returns in 24 months.
What does the CAC Payback Period Calculator calculate, and which formula does it use?
The CAC Payback Period Calculator divides customer acquisition cost by monthly gross profit (ARPU × gross-margin percentage) to find how many months revenue takes to repay CAC. It also estimates a 24-month LTV and LTV:CAC ratio, then grades payback (≤6 excellent, ≤12 good, ≤18 caution, otherwise danger) and the ratio (≥5 excellent, ≥3 good).
Last updated .
How to use it
- Enter CAC, monthly ARPU, gross margin percentage, and an optional target payback period such as 12 months. Use your own gross margin (listed US software averaged 71.7% in Damodaran's January 2026 data) and a payback target you can finance from cash on hand.
- Read payback months, monthly gross profit, gross profit over the first 24 months, the 24-month return on CAC, the gap versus your target, and the guidance line under the result. Payback of 6 months or less is excellent, up to 12 months is good, 12-18 months needs caution, and more than 18 months is a danger zone.
- Read the 24-month return as a payback check, not a lifetime value: it equals 24 ÷ payback months, so 3× means payback within 8 months. If the return looks weak, model lifetime value with your real churn in the CAC calculator before deciding whether retention or acquisition is the limiting factor.
- Act on the guidance by choosing the right lever: cut CAC, improve ARPU, raise gross margin, or pause heavy acquisition until onboarding and retention improve. If you are ahead of target by several months, that is an argument for increasing spend, not just celebrating efficiency.
- Re-run monthly by acquisition channel and cohort. Track payback against actual gross-margin changes over time because delivery-cost creep can quietly stretch the recovery period even if topline ARPU looks stable.
Questions people usually ask
What is CAC payback period?
CAC payback period is the number of months it takes to recover your customer acquisition cost from the gross profit that customer generates each month. Formula: CAC ÷ (Monthly ARPU × Gross Margin %).
What is a good CAC payback period?
David Skok's SaaS Metrics 2.0 draws the line at 12 months: beyond that, profitability is anemic, and many of the best SaaS businesses recover CAC in 5-7 months. This tool labels up to 6 months Excellent, up to 12 Good, up to 18 Caution and anything longer Danger. Capital-intensive or enterprise businesses may tolerate longer periods.
What is a good LTV:CAC ratio?
David Skok's guideline for SaaS is above 3×, with the best businesses reaching 7× or 8×; this tool labels 3× Good and 5× or higher Excellent. Below 1× a customer is worth less than it cost to acquire, and 1× to 1.5× leaves little room once overhead is counted. This tool's ratio uses 24 months of gross profit, so it equals 24 ÷ payback months; for lifetime value with churn, use the CAC calculator.
Why does this tool use a 24-month LTV horizon?
24 months is a commonly used horizon for early-stage SaaS to avoid overestimating value from uncertain long-term retention. The figure assumes the customer stays all 24 months with no churn, so it is a payback check rather than a true lifetime value. For businesses with known cohort data, model LTV with your churn in the CAC calculator.
How is monthly gross profit calculated?
Monthly Gross Profit = Monthly ARPU × (Gross Margin % ÷ 100). This is the profit contribution per customer per month after cost of goods sold or service delivery costs.
Is this tool free and private to use?
Yes. AI Biz Hub tools run entirely in your browser with no signup required. Inputs stay local unless you share the URL.
Is this professional advice?
No. Outputs are planning estimates — not financial, legal, or accounting advice. Validate with your actual cohort data and an advisor.
The same numbers as a table
- Reference CAC payback months by monthly ARPU and acquisition cost
Precomputed by this calculator across common inputs, to cite or download as CSV.
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Use it from code
The same calculation as a JavaScript module you can import. It runs where you import it, with no request, key or rate limit.
import { compute } from "https://aibizhub.io/engines/cac-payback-calculator.js";Input and output contract, TypeScript types and the guide for agents.