Free calculator · Venture & Startup Finance
Unit Economics, CAC · LTV · LTV:CAC · Payback
Calculates customer acquisition cost, customer lifetime value, the LTV:CAC ratio, and the CAC payback period for a subscription business. Inputs are monthly revenue per customer, gross margin, monthly churn, sales and marketing spend, and new customers per month.
By Devon Coombs, CPA, MBA · Teaching Professor of Finance, Santa Clara University · Reviewed August 2026
From the author: Devon Coombs, CPA, MBA teaches finance at Santa Clara University and works with corporate teams on practical AI.
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Unit Economics, CAC · LTV · LTV:CAC · Payback
CAC
$2,000
cost to win one customer
Avg lifespan
35.7 mo
1 ÷ monthly churn
LTV
$5,714
ARPU × margin × lifespan
CAC payback
12.5 mo
< 12 mo strong · > 18 risky
LTV : CAC
2.86 : 1
Below the 3:1 SaaS benchmark
Churn is the silent killer: nudge monthly churn from 2.8% to 6% and watch lifespan roughly halve, dragging LTV:CAC toward break-even while price, margin, and CAC never move.
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This calculator comes from the free Entrepreneurial Finance course, where the concept is taught with readings, worked examples, and practice questions.
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Built by Devon Coombs, CPA, MBA, Teaching Professor of Finance at Santa Clara University.