# SaaS Unit Economics for Founders: CAC, LTV, ARPU and Payback

> A founder-friendly guide to the small set of SaaS metrics that shows whether growth is creating durable gross profit or consuming cash.

- URL: https://www.pyalm.com/blog/saas-unit-economics-founder-guide
- Author: Fadhil Abdulla
- Category: Founder Guides
- Published: 2026-07-20
- Updated: 2026-07-20

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Revenue growth looks healthy only when the economics underneath it are healthy. Four metrics give founders a fast first view: ARPU, customer acquisition cost, lifetime value, and CAC payback.

## ARPU: revenue per active customer

`Monthly ARPU = MRR ÷ active customers`

If monthly recurring revenue is AED 100,000 from 250 customers, ARPU is AED 400. Segmenting ARPU by plan or customer type is more useful than relying only on the blended average.

## CAC: the cost to win a customer

`CAC = sales and marketing spend ÷ new customers acquired`

Use costs and acquisitions from the same period. A fuller CAC includes paid media, sales salaries, commissions, tools, agencies, and attributable content costs. Excluding sales payroll can make acquisition look artificially efficient.

## LTV: expected gross profit over a customer life

A common quick model is:

`LTV = monthly ARPU × gross margin % ÷ monthly customer churn %`

At AED 400 ARPU, 80% gross margin, and 4% monthly churn, the estimate is AED 8,000. This formula assumes a stable churn rate. It is directional and becomes less reliable when cohorts behave differently or churn is volatile.

## LTV:CAC and CAC payback

LTV:CAC compares estimated gross-profit value with acquisition cost. A 3:1 result means the model expects three dirhams of lifetime gross profit for each dirham spent acquiring the customer.

CAC payback asks a cash question:

`CAC payback months = CAC ÷ monthly gross profit per customer`

A business can show an attractive LTV:CAC ratio and still face a cash squeeze if payback is slow. That is why both measures belong in the same review.

Use the free [SaaS Unit Economics Calculator](https://www.pyalm.com/free-tools/saas-unit-economics-calculator) to calculate all five outputs together.

## Review by cohort, not only as a company average

Blended metrics can hide important differences. Compare customers by acquisition month, channel, plan, geography, and company size. A channel with low CAC but high early churn may be worse than a more expensive channel that retains customers for years.

## A useful monthly founder review

Ask four questions:

1. Did CAC change because spend changed or conversion changed?
2. Did payback improve because ARPU or gross margin improved?
3. Is churn concentrated in a plan, cohort, or onboarding path?
4. Are expansion and referrals lowering the effective cost of growth?

The point is not to celebrate a benchmark. It is to find the operating lever that changed and decide what to do next.