Break-Even CPA Calculator

Your maximum cost per acquisition

Break-even CPA is the dollar amount at which an order is worth exactly nothing to you. One cent more and you are paying for the privilege of shipping something.

Break-even CPA = AOV × contribution margin

Contribution margin is what is left of an order after every cost that is not advertising: landed cost including duty, platform commission, payment processing, fulfilment and returns. Whatever remains is the entire budget available to buy that order.

This is the same fact as break-even ROAS wearing different units. ROAS is a ratio you set as a bid target; CPA is a dollar figure you compare against the cost per purchase in your dashboard. Use whichever matches how you actually make decisions — and if your AOV moves around, prefer ROAS, because a fixed CPA ceiling silently gets stricter as basket sizes fall.

Two ways to enter it

Contribution margin, if you already know it

Fastest route. Type the percentage and you have your ceiling. The risk is that most people’s remembered margin is gross margin, which excludes shipping, payment fees and returns — and is therefore far too generous.

The full cost breakdown

Slower and more honest. Landed cost, fulfilment shipping, platform fee and return rate, and the calculator derives contribution margin for you. If the two routes disagree, the breakdown is right.

Average order value

Use your actual AOV, not your headline product price. If bundles or quantity discounts move real basket size away from list price, the ceiling moves with it.

A worked example

A $49 order with $15.83 landed cost, $5.50 fulfilment shipping, no marketplace fee, 2.9% + $0.30 payments and a 6% return rate at full loss.

Contribution margin works out at 47.0%, so break-even CPA is $23.01. Pay more than that for an order and it loses money. The equivalent break-even ROAS is 2.13x.

Now try the shortcut. Gross margin on this SKU — price minus landed cost only — is 67.7%, which would suggest a $33.17 ceiling. Acting on that number, you would overpay by $10.16 on every order while believing you were profitable. That gap is the entire reason to expand the breakdown.

Comparing it against your dashboard

The comparison to make is your break-even CPA against your actual cost per purchase — but not the one the ad platform reports. Platform CPA is computed against orders the platform believes it caused, and when two platforms both claim the same order, both report a flattering number.

Use total ad spend divided by total orders instead. It is a blunter figure and a truthful one. If that number sits above your break-even CPA, the account is unprofitable no matter how good any individual campaign looks.

One caution about the ceiling itself: it assumes a customer buys once. If you have real repeat purchase behaviour, your economics support a higher first-order CPA — but only if you have measured the repeat rate rather than hoped for it.

Next steps

Questions

Is break-even CPA the same as CAC?

Related but not identical. CAC is what you actually paid to acquire a customer, historically. Break-even CPA is the ceiling above which acquiring one destroys value. One is a measurement, the other is a constraint — you compare the first against the second.

Should I use gross margin or contribution margin?

Contribution margin, always. Gross margin stops at cost of goods and ignores shipping, payment fees and returns. On the example above it overstates your ceiling by $10.16 per order — enough to make an unprofitable account look healthy for a whole quarter.

Can I pay above break-even CPA if customers reorder?

Yes, and that is the main legitimate reason to. But it requires a measured repeat rate and a known second-order margin, not an assumption that people will come back. Paying above break-even on the strength of an unmeasured lifetime value is the most expensive optimism in ecommerce.

How do tariffs change my break-even CPA?

Duty lands in cost of goods, which reduces contribution margin, which lowers the ceiling proportionally. On the example SKU, the 2026 duty stack takes $3.43 straight out of the $23.01 you had to spend acquiring each order — about 13% of the entire acquisition budget, gone before you write an ad.

Why does my calculated CPA differ from the platform's target CPA field?

Because the platform optimises toward its own attributed conversions, while your ceiling is derived from money that actually arrived. Set the platform target below your true ceiling, then verify against total spend divided by total orders. Treat the platform figure as a steering input, not as truth.

Sources and last update

Last verified 2026-08-22.

• USITC Harmonized Tariff Schedule — MFN general rates
• USTR — Section 301 forced labor actions

Figures here are planning estimates. Duty applies per 10-digit HTS code and platform fees change without much notice — check your own broker and your own seller account before committing spend. Full workings on the methodology page.