InterLAB tools · Live charts · scenarios · 3:1 goal

Unit economics calculator

Move the sliders and see right away what a customer brings, when ads pay back, when the business turns profitable and how long the cash lasts. Formulas are shown with your numbers; the sensitivity chart shows which input moves the result the most.

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How it works

Business model
A preset fills in typical illustrative values (not industry norms) — replace them with yours. Currency is a label only; amounts are not converted.
Unit and customer
A unit is a subscription month or one order. Price and margin give the contribution; churn or the repeat rate give lifetime and LTV; budget and new customers give CAC.
A 36-month model
Each month a new cohort arrives (growing by the given %), older cohorts shrink with retention. Monthly result = contribution of all cohorts − marketing − fixed costs; this gives break-even and runway.
Sensitivity, goal, scenarios
The tornado shows how LTV:CAC, payback or the 36-month result change with ±10/20% of each input. The solver answers how much one input must change for LTV:CAC to reach the goal. Scenarios are saved as versions and compared side by side.

Subscription (SaaS) — Monthly ARPU, churn
E-commerce — Order value, repeat orders
Marketplace — GMV, take rate
Services / agency — Retainer per month
Mobile app — ARPU, store fee in margin

Formulas and definitions

The tables are generated from the same code as the calculation. LTV is based on margin (contribution), not revenue: revenue without costs overstates a customer's value.

ID	Metric	Formula	Notes
F1	Contribution per unit	Net revenue − variable cost; margin = contribution / net revenue	A unit is a subscription month or one order. For a marketplace, net revenue = GMV × take rate.
F2	CAC	Marketing and sales per month / new customers per month	Or enter CAC directly. Include everything spent on acquisition: ads, sales, first-order discounts, partner fees.
F3	LTV (margin-based)	Subscription: ARPU × margin / churn. E-commerce: order contribution / (1 − repeat rate)	It is the geometric series contribution × Σ qʲ, where q is retention per step. The month a customer joins counts as paid.
F4	LTV with discounting and a lifetime cap	contribution × (1 − q^J) / (1 − q), q = retention / (1 + d)^step, d = (1 + annual rate)^(1/12) − 1	J is the number of steps within the cap. With 0% churn and no cap of your own, LTV is capped at 60 months (UE-W01).
F5	LTV:CAC	LTV / CAC	The bands are a heuristic (see the table below), not a universal norm.
F6	CAC payback	Classic: CAC / (contribution per month). Cohort: the first month when a customer's cumulative expected contribution ≥ CAC	The classic formula ignores churn; the cohort one includes it and may never happen (UE-W06).
F7	Break-even point	Fixed costs / contribution per active customer per month (for a store — / order contribution)	How many active customers (or orders per month) cover fixed costs — excluding marketing.
F8	Monthly model and runway	Monthly result = contribution of all cohorts − marketing − fixed costs; cash = starting cash + cumulative result	New customers grow by the given % per month, CAC is constant. Runway is the month cash first goes negative.

Metric: Contribution per unit
Formula: Net revenue − variable cost; margin = contribution / net revenue
Notes: A unit is a subscription month or one order. For a marketplace, net revenue = GMV × take rate.

Metric: CAC
Formula: Marketing and sales per month / new customers per month
Notes: Or enter CAC directly. Include everything spent on acquisition: ads, sales, first-order discounts, partner fees.

Metric: LTV (margin-based)
Formula: Subscription: ARPU × margin / churn. E-commerce: order contribution / (1 − repeat rate)
Notes: It is the geometric series contribution × Σ qʲ, where q is retention per step. The month a customer joins counts as paid.

Metric: LTV with discounting and a lifetime cap
Formula: contribution × (1 − q^J) / (1 − q), q = retention / (1 + d)^step, d = (1 + annual rate)^(1/12) − 1
Notes: J is the number of steps within the cap. With 0% churn and no cap of your own, LTV is capped at 60 months (UE-W01).

Metric: LTV:CAC
Formula: LTV / CAC
Notes: The bands are a heuristic (see the table below), not a universal norm.

Metric: CAC payback
Formula: Classic: CAC / (contribution per month). Cohort: the first month when a customer's cumulative expected contribution ≥ CAC
Notes: The classic formula ignores churn; the cohort one includes it and may never happen (UE-W06).

Metric: Break-even point
Formula: Fixed costs / contribution per active customer per month (for a store — / order contribution)
Notes: How many active customers (or orders per month) cover fixed costs — excluding marketing.

Metric: Monthly model and runway
Formula: Monthly result = contribution of all cohorts − marketing − fixed costs; cash = starting cash + cumulative result
Notes: New customers grow by the given % per month, CAC is constant. Runway is the month cash first goes negative.

Formulas (v1.0, 2026-10-14)

Contribution margin is net revenue minus variable cost per unit. Fixed costs are not part of LTV — they are in the monthly model.
Churn is the share of customers who leave in a month; expected lifetime = 1 / churn months (at 4% — 25 months).
Discounting: the annual rate becomes a monthly d = (1 + r)^(1/12) − 1; month k's contribution is multiplied by 1 / (1 + d)^k.
Classic payback is CAC / contribution per month, without churn (the usual definition); cohort payback includes churn, so it is longer or never happens.
Break-even in customers ignores marketing; the first profitable month and runway include it (monthly model).

ID	LTV:CAC	Band	What it means
UE-B1	< 1	Customers do not pay back	A customer brings less contribution than it costs to acquire: growth deepens the loss.
UE-B2	1 – 3	Thin economics	Customers pay back, but the margin of safety is small: little may remain after fixed costs.
UE-B3	3 – 5	Common benchmark	3:1 and above is a common benchmark for subscription businesses. It is a heuristic, not a law: check the payback period too.
UE-B4	≥ 5	Growth may be underfunded	A very high ratio may mean you spend less on acquisition than you could — or that LTV is inflated by assumptions.

UE-B1

LTV:CAC: < 1
Band: Customers do not pay back
What it means: A customer brings less contribution than it costs to acquire: growth deepens the loss.

UE-B2

LTV:CAC: 1 – 3
Band: Thin economics
What it means: Customers pay back, but the margin of safety is small: little may remain after fixed costs.

UE-B3

LTV:CAC: 3 – 5
Band: Common benchmark
What it means: 3:1 and above is a common benchmark for subscription businesses. It is a heuristic, not a law: check the payback period too.

UE-B4

LTV:CAC: ≥ 5
Band: Growth may be underfunded
What it means: A very high ratio may mean you spend less on acquisition than you could — or that LTV is inflated by assumptions.

LTV:CAC bands (a heuristic)

The 3:1 benchmark and CAC payback within 12 months are common heuristics for subscription businesses (for example, David Skok's “SaaS Metrics 2.0”, forentrepreneurs.com). They are not universal: a store with one-off purchases, a service with a long sales cycle or a business with cheap capital will have different reasonable values.

ID	When and what
UE-W01	0% churn (or 100% repeat) means an infinite lifetime. LTV is capped at 60 months; set your own cap.
UE-W02	Contribution per unit is negative: every sale adds to the loss, there is no payback.
UE-W03	CAC = 0: LTV:CAC is infinite. Check you have not left out sales, discounts, partner fees and team time.
UE-W04	No new customers — CAC cannot be derived from the budget. Enter new customers per month or CAC directly.
UE-W05	Churn above 20% a month: half the customers leave within 3 months — fix retention before buying ads.
UE-W06	Cohort payback never happens: with churn, a customer leaves before returning the CAC.
UE-W07	CAC payback is longer than 12 months: growth will need a lot of working capital.
UE-W08	Margin above 95% — check that payment fees, hosting, support and commissions are included.

UE-W01

When and what: 0% churn (or 100% repeat) means an infinite lifetime. LTV is capped at 60 months; set your own cap.

UE-W02

When and what: Contribution per unit is negative: every sale adds to the loss, there is no payback.

UE-W03

When and what: CAC = 0: LTV:CAC is infinite. Check you have not left out sales, discounts, partner fees and team time.

UE-W04

When and what: No new customers — CAC cannot be derived from the budget. Enter new customers per month or CAC directly.

UE-W05

When and what: Churn above 20% a month: half the customers leave within 3 months — fix retention before buying ads.

UE-W06

When and what: Cohort payback never happens: with churn, a customer leaves before returning the CAC.

UE-W07

When and what: CAC payback is longer than 12 months: growth will need a lot of working capital.

UE-W08

When and what: Margin above 95% — check that payment fees, hosting, support and commissions are included.

Warnings

Limitations

The model is linear: CAC does not rise with budget, churn does not change over time or by cohort, there is no seasonality. Check the assumptions against your own data before big decisions.
Customers at start are modelled with retention only (no lifetime cap); for a store their orders are spread evenly across the interval.
Taxes, working capital (inventory, payment terms), refunds and fundraising are not modelled.
The goal solver changes one input, all else equal; in reality inputs are linked (a higher price usually raises churn).
With 0% churn (or a 100% repeat rate) and no cap of your own, LTV is capped at 60 months — otherwise it is infinite.

Privacy

All calculations run in your browser: calculating never sends the numbers to a server or puts them in the page address.
Inputs and scenario versions are stored only in this browser's localStorage; “Clear all” deletes them. Exports are files: Markdown or PDF with all formulas and assumptions, a CSV of the monthly model, JSON for re-import.
Analytics receives only the fact of a calculation with categories (business model, LTV:CAC band, payback range) or the export format — none of your numbers.
The result reaches us only if you send a request yourself and keep the “Attach the result” box ticked — the form shows exactly what will be sent. Until you change the default values there is nothing to attach.

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