Customer Acquisition Cost Calculator
Bridge the gap between cost per order and cost per NEW customer, then test whether a new customer pays you back inside your payback window — the two numbers every acquisition budget is really judged on.
Customer Acquisition Cost Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Ad-account scope only — no payroll, tools or overhead.
- New-customer share must come from the same period as the spend.
- The 90-day window is a default, not a law; say which window you underwrite.
In short: CPA counts orders; CAC counts new customers. 24,975 of spend buys 518 orders but only 321.16 of them are new, so CPA is 48.21 and CAC is 77.76 — a 29.55 gap — and at 53.76 contribution a new customer must reorder 1.45 times before the acquisition pays.
Formula
CPA = spend ÷ orders
CAC = spend ÷ (orders × new-customer share)
payback: CAC ≤ contribution × orders per customer
[('CPA', 'cost per ORDER — what the platform reports'), ('CAC', 'cost per NEW CUSTOMER — what the business bought'), ('share', 'the only thing that bridges them'), ('window', '90 days here; hold every channel to the same one')]
Worked Example
- Divide spend by total orders for the platform-facing CPA.
- Multiply orders by the new-customer share to isolate demand you created.
- Divide the same spend by new customers for the true CAC.
- Multiply contribution per order by orders per customer for window value.
- Compare CAC to the window value for the payback verdict.
24,975 of spend buys 518 orders — a 48.2143 CPA. At a 62% new-customer share only 321.16 of those orders are new customers, so the true CAC is 77.7650 and the gap is 29.5507. A 53.76 contribution order repeated 1.35 times in 90 days returns 72.576 per new customer: 5.1890 short of payback, which is why the channel needs a 1.4465 repeat rate, not a cheaper click.
Strengths & Limits Of This Model
Where this engine is strong
- Bridges CPA to CAC with one measurable share
- Prices the payback gap instead of a pass/fail
- Refuses to mix loaded costs into the bridge
Where it stops
- Blind to load beyond the ad account
- Fractional customers read oddly at small scale
Practical Use Cases
Budget caps that survive scrutiny
Cap on CAC, not on the platform's CPA.
Channel comparisons
One payback window across every channel.
Retargeting audits
See what cheap retargeting orders do to the bridge.
Forecasting cash
A CAC outside the window is financed growth.
Agency accountability
Judge the agency on customers bought, not orders placed.
Methodology & Editorial Standards
CPA is spend over orders. CAC is the same spend over expected new customers, bridged only by the new-customer share, so the two agree by construction: CAC equals CPA divided by the share, always. The payback test compares CAC with contribution per order multiplied by orders per customer inside a 90-day window, and the page reports the ceiling (the window value itself) and the break-even repeat rate rather than a single pass/fail. Loaded costs are excluded on purpose; the business-side CAC is a different page with different fields, and the suite asserts the boundary both ways.
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Customer Acquisition Cost Calculator — 10 Expert FAQs
10 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
What is the difference between CPA and CAC?
CPA divides spend by all orders. CAC divides the same spend by new customers only. They are bridged by the new-customer share: at 62% share, CAC is CPA divided by 0.62, which is 61% higher. The ad platform can only see orders, so it always reports the flattering one.
Why is my reported CPA much lower than my real CAC?
Because a share of those orders came from existing customers who needed no acquisition. Retargeting, brand search and coupon affiliates are the usual inflators. Divide CPA by the new-customer share and the gap appears in one step.
What share of orders should come from new customers?
There is no target — the share is a measurement input, not a kPI. What matters is that the share is measured the same way on both sides of any comparison, because the whole CPA-to-CAC bridge moves with it.
What is a good CAC payback window?
Whichever window your cash flow can finance. Ecommerce businesses commonly test 90 days; subscription businesses use monthly gross profit and think in months. The discipline matters more than the number: every channel should be judged on the SAME window.
Should payroll and overhead be inside CAC?
For total business CAC, yes — loaded CAC includes the team and tools that make acquisition possible. This page deliberately stops at the ad-account boundary so the CPA-to-CAC bridge stays clean; the loaded build belongs to the business-side model.
Does a CAC above first-order contribution mean the channel fails?
No — it means the channel is financed by repeat purchases. Most healthy acquisition works that way. The failure mode is a CAC above first-order contribution AND a repeat rate that never closes the gap inside the window you can finance.
How do I raise the repeat rate?
The levers are post-purchase: replenishment reminders, bundles on the second order, and a returns experience that does not end the relationship. Acquisition-side optimisation cannot move it, which is why a channel verdict needs both numbers on this page.
Why does CAC use fractional customers?
Because it is an expectation: 518 orders at 62% is 321.16 expected new customers. Rounding to whole customers makes small-period CACs jump around and hides trends; the fraction is the honest figure over the window.
Can I compare CAC across channels with different windows?
Not safely. A 30-day window flatters channels that convert fast and punishes channels whose customers reorder slowly. Fix one window for the whole portfolio and re-derive every channel against it.
Where does blended CAC fit?
Blended CAC divides TOTAL spend — including brand and content — by all new customers. It answers a different question from the channel-level bridge on this page, and both sit below the loaded, business-side CAC that adds payroll and overhead.