SYS/RES

Calculators

Value of a test, acquisition, traffic and SEO — growth arithmetic.

Test EV CPA / ROAS LTV:CAC Traffic goal SEO traffic

LTV:CAC and payback

LTV:CAC ratio and the number of months before acquisition pays itself back. Growth economics, distinct from A/B maths and often more decisive.

SYS/IN

A simple model — not a cohort engine. LTV is an input, not a retention curve.

LTV (lifetime value)Customer lifetime value, in euros. €

CAC (customer acquisition cost)Cost to acquire one customer, in euros. Zero → ratio undefined. €

Lifetime (months)Used to derive monthly contribution when the next field is 0.

Monthly contribution (optional)Monthly margin per customer. Leave 0 to use LTV / lifetime. €

SYS/OUT

LTV:CAC ratio

4.0 : 1

LTV / CAC

Payback months: 6.0 months
Monthly contribution: €20.00

How this is calculated

Formulas

Two outputs:

LTV:CAC ratio = LTV / CAC. A ratio of 4 displays as 4.0 : 1.
Payback months = CAC / monthly contribution.

Monthly contribution is, in order:

the entered monthly margin if it is > 0;
otherwise LTV / lifetime in months.

Equivalent when derived: payback = CAC × lifetime / LTV.

If CAC is 0, the ratio is undefined. If monthly contribution is 0, payback is undefined. The tool shows a dash, not Infinity.

Sources

Classic growth unit-economics (SaaS / e-commerce). This is not an academic paper: it is the napkin model you sketch before opening a cohort spreadsheet.

Limits

Not a cohort engine. LTV is an input, not a discounted sum of retention × basket × margin.
No churn curve, no discount rate, no gross vs net margin.
A flat monthly contribution is a strong assumption — real profiles pay more up front or erode.
A 3:1 ratio is not a verdict; it is an order of magnitude to cross-check against payback and cash.