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How many months does it take for a new customer's gross profit to repay the cost of acquiring them? Customer-acquisition-cost payback is the canonical per-customer SaaS efficiency metric. Classified into the standard bands (<6mo exceptional · 6-12 great · 12-18 good · 18-24 OK · >24 bad), with gross-margin built in so the number reflects actual contribution, not raw revenue.
CAC payback is how many months it takes for the gross profit from a customer to repay the cost of acquiring them. Formula: CAC / (monthly ARPC × gross margin %). Lower is better. It is the customer-level efficiency metric in the same family as magic number (cohort-level) and burn multiple (company-level).
Roughly: <6 months exceptional (best-in-class PLG and infra SaaS), 6-12 months great (top quartile), 12-18 months good (typical Series B+ enterprise SaaS), 18-24 months OK (acceptable at scale, watch trajectory), >24 months bad (most growth-stage investors will pass). Enterprise SaaS sits at the longer end; PLG / infra SaaS pulls toward the shorter end.
All three measure SaaS efficiency from different angles: CAC payback is per-customer, magic number is per-cohort GTM input, burn multiple is the whole company's burn vs ARR. Healthy companies score well on all three. Discrepancies are diagnostic — great burn multiple + 25-month CAC payback means efficient on average but reliant on unhealthy long-tail customers; great CAC payback + poor magic number means each customer is profitable but the motion isn't scaling.
Revenue ≠ profit. A customer paying $1,000/mo at 75% gross margin contributes $750/mo of gross profit; at 40% margin only $400/mo. Payback uses gross contribution, not revenue, because cost of revenue (hosting, support, payment processing, licensing) has to come out before any of it can pay back CAC. Healthy SaaS gross margin sits at 70-80%; lower margins push payback out proportionally.
CAC is undefined when zero new customers were acquired — there is no cost per customer to compute. The calculator flags this state explicitly. If you find yourself there, the diagnostic question is whether the spend produced no customers or whether the period was just too short to see them land.
Yes — every input is encoded in the URL. The 'Copy share link' button copies the current URL to your clipboard. Send it to your board, head of sales, or growth-stage investor and they open the calculator with the same numbers.
Healthy companies score well on all three. Discrepancies are diagnostic.
Whole-company
Total burn / net new ARR. Sacks bands.
Per-cohort GTM
Annualized net new ARR / quarterly S&M. Bessemer bands.
Per-customer · you are here
CAC / (monthly ARPC × GM%). Standard bands.
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CAC payback
13.3 months
Good — typical Series B+ enterprise SaaS.
CAC
$10k
S&M spend / new customers.
Monthly gross contribution
$750
ARPC/12 × gross margin %.
ARPC (monthly)
$1k
Annual ARPC divided by 12.
Bands: <6mo exceptional · 6-12 great · 12-18 good · 18-24 OK · >24 bad. Enterprise SaaS sits at the longer end; PLG / infra SaaS pulls to the shorter end.
Why this metric: CAC payback is the customer-level efficiency view, in the same family as magic number (cohort-level) and burn multiple (company-level). All three should be looked at together. A great burn multiple with 25-month CAC payback means the company is efficient on average but relies on unhealthy long-tail customers; a great CAC payback with poor magic number means each customer is profitable but the GTM motion isn't scaling.
The URL contains your inputs — drop into a board deck or investor update without retyping.
Educational tool. Real diligence pairs CAC payback with net dollar retention, LTV/CAC, and churn cohorts. Not financial planning advice.