How to Calculate Your Break-even CAC

What break-even CAC means

CAC is what you spend in a given period to acquire customers (1). Your break-even CAC is the most you can pay to acquire one new customer without losing money on them. Go above it and every new customer costs you more than they leave behind.

The ceiling depends on two questions. How much is left from each order after variable costs? How many orders do you expect from one customer? Shopify says CAC is most useful when compared with what customers spend over their whole relationship with the brand, the LTV/CAC ratio (1). So it helps to calculate two ceilings: a strict one based on the first order, and a wider one based on LTV.

Step 1: Work out your margin after variable costs

Start from the selling price and subtract every cost that repeats with each order:

• The cost of the goods themselves (2).
• Shipping and packaging (3).
• Payment processing fees (3).
• Warehouse pick-and-pack fees (3).

Then calculate margin as (revenue minus variable costs) divided by revenue (4). In Shopify's example, a product sells for $100 and its variable costs come to $60, giving a 40% margin (2). That leaves $40 per order to cover acquisition and profit.

Use the fees you actually pay for each payment method you offer, not a rough average. Payment processing fees are a core part of variable cost (3).

Step 2: Account for returns

Your margin is not complete until you account for returns. A returned order loses its revenue, while you have probably already paid its shipping, packaging and pick-and-pack costs (3). So calculate margin on the orders customers actually kept, not on every order that left the warehouse.

For context only, one report estimated that 19.3% of US online sales would be returned in 2025, against 15.8% of total retail sales (5). That figure is no substitute for your own rate, so use the rate in your own data. Another report puts about 9% of all returns down as fraud, such as empty boxes and label tampering (6). That is an extra cost worth tracking.

Step 3: Turn the margin into a CAC ceiling

Once you know your net margin, you can calculate both ceilings:

• First-order ceiling = average order value × margin after returns. This is the point where a customer pays back their acquisition cost on the first order.
• LTV-based ceiling = the total margin you expect across all of a customer's orders over their relationship with the store. It gives you more room to spend, but it depends on forecasting repeat purchases (1).

In Shopify's example, if the customer buys only once, the ceiling is about $40 per new customer (2). You can express the same margin as ROAS by dividing 1 by the margin (4), which gives a break-even ROAS of 2.5 in that example (2).

The lower the margin, the higher the ROAS you need to break even. In an example shown by Google, a 15% margin corresponds to a 667% Target ROAS at break-even (7).

Measure your real CAC before comparing

A ceiling is useless if you compare it against an incomplete number. Shopify calculates CAC as total sales and marketing spend divided by the number of new customers. It warns that counting ad spend alone understates CAC (8). Include:

• Ad spend across every platform.
• Creative production (8).
• Agency and consultant fees (8).
• Marketing software (8).
• Team time (8).

Leave out retention spend such as loyalty programs, win-back campaigns and post-purchase emails, along with fulfillment and customer service costs (9). These belong to existing customers or to variable costs, not to acquiring new ones.

Use the ceiling to judge campaigns

With the ceiling and your real CAC in hand, judging campaigns becomes clearer:

• Compare each campaign's actual CAC with the first-order ceiling. A campaign below it is profitable on the first order. A campaign between the two ceilings depends on repeat purchases, so watch it closely.
• Translate the ceiling into a platform Target ROAS. A 500% Target ROAS means every $1 spent on ads should bring in $5 of revenue (10).
• Do not accept the platform's suggestion without checking it. Google Ads bases its recommended Target ROAS on the campaign's actual ROAS over the last few weeks, and you can set your own (11). Recent performance says nothing about your margin.
• Enter the margin correctly. In Google's test calculator, you enter the average profit margin excluding ad spend, and Google assumes the reported conversion value is revenue, not profit (12).
• Read results over a complete date range. Google advises leaving the most recent conversion-delay period out, so performance is read accurately (13).

Remember that platform ROAS only measures ad spend, while your real CAC includes other costs (8). A campaign that hits break-even ROAS on the platform can still be losing money, so leave a safety margin above the break-even number.

Sources

1. (1) Shopify · 2026-11-06
2. (2) Shopify · 2026-09-02
3. (3) Shopify · 2026-09-02
4. (4) Shopify · 2026-09-02
5. (5) National Retail Federation · 2025-10-15
6. (6) UPS · 2025-12
7. (7) Search Engine Land · 2026-10
8. (8) Shopify · 2026-07
9. (9) Shopify · 2026-07
10. (10) Google · 2026-06
11. (11) Google · 2026-06
12. (12) Search Engine Land · 2026-10
13. (13) Google · 2026-06

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