ROAS, CAC, Break-even ROAS and MER: Formulas and Examples
Formulas and worked examples for ROAS, CAC, break-even ROAS and MER, with a clear guide to which metric to optimise for at each stage of growth.
Quick answer: ROAS is ad revenue divided by ad spend. CAC is total acquisition cost divided by new customers. Break-even ROAS is 1 divided by your contribution margin percentage. MER is total revenue divided by total marketing spend. Use break-even ROAS as the floor for campaigns, MER to judge the whole business, and CAC against customer lifetime value to decide how fast to grow.
ROAS, CAC, break-even ROAS and MER are the four numbers most founders and marketing leads use to judge paid media. They are often quoted without formulas, mixed up with each other, or compared across businesses with very different margins.
This guide gives you each formula, a worked example using one simple illustrative brand, and a clear view on which metric to optimise for at each stage of growth.
Key takeaways
- ROAS tells you how efficient a campaign or channel is, but says nothing about profit on its own.
- Break-even ROAS comes from your contribution margin, so every business has a different one.
- MER (blended ROAS) uses total revenue and total marketing spend, so it does not depend on platform attribution.
- CAC only makes sense next to customer lifetime value and payback period.
- Optimise campaigns against break-even ROAS, and run the business on MER and CAC.
What are ROAS, CAC, break-even ROAS and MER?
| Metric | Formula | What it answers | Level |
|---|---|---|---|
| ROAS (return on ad spend) | Revenue from ads / Ad spend | How much revenue did this campaign return per rupee spent? | Campaign, ad set, channel |
| CAC (customer acquisition cost) | Total acquisition costs / New customers | What does it cost to win one new customer? | Channel or business |
| Break-even ROAS | 1 / Contribution margin % | What ROAS do I need so that ads do not lose money? | Business, applied to campaigns |
| MER (marketing efficiency ratio) | Total revenue / Total marketing spend | How efficient is all marketing combined? | Business |
These definitions follow the standard formulas used by platforms and analytics tools. Shopify’s guide to the ROAS formula defines ROAS as revenue from ads divided by ad spend, and its customer acquisition cost guide defines CAC as total acquisition costs in a period divided by new customers in that period.
How do you calculate ROAS?
Formula: ROAS = Revenue attributed to ads / Ad spend
All the numbers below are simple illustrative examples for one fictional D2C brand, not benchmarks.
Example: A Meta campaign spends ₹1,00,000 in a month and the platform attributes ₹3,00,000 in revenue to it. ROAS = 3,00,000 / 1,00,000 = 3.0, often written as 3x or 300%.
Google Ads expresses the same idea as a percentage. Its help page on Target ROAS bidding uses the example of $5 in sales for every $1 of ad spend, which equals a 500% target ROAS.
ROAS is useful for comparing campaigns, ad sets and creatives inside one platform. Its weakness is that it depends on attribution. Meta and Google can both claim credit for the same order, so the sum of platform-reported revenue is often higher than your actual store revenue.
How do you calculate break-even ROAS?
Formula: Break-even ROAS = 1 / Contribution margin %
Contribution margin is what is left from each sale after the cost of the product and all variable costs of fulfilling the order, before marketing. Variable costs usually include shipping, packaging, payment gateway fees, marketplace or app fees, and an allowance for returns.
Example: Average order value is ₹2,000. Product cost is ₹800. Shipping, packaging, payment fees and a returns allowance add up to ₹300 per order.
Contribution per order = 2,000 minus 800 minus 300 = ₹900.
Contribution margin = 900 / 2,000 = 45%.
Break-even ROAS = 1 / 0.45 = 2.22 (or 222% as a Google Ads target).
At a ROAS of 2.22, each ₹1 of ad spend brings in exactly enough contribution to pay for itself. Below 2.22, the campaign loses money on the first order. Above it, the campaign is profitable on the first order.
Checking the campaign from the ROAS example
Our campaign had a ROAS of 3.0 on ₹1,00,000 of spend. Contribution = ₹3,00,000 × 45% = ₹1,35,000. After subtracting ₹1,00,000 of ad spend, the campaign made ₹35,000 in contribution profit, before fixed costs such as salaries and rent.
The same 3.0 ROAS would lose money for a brand with a 30% contribution margin, because that brand’s break-even ROAS is 1 / 0.30 = 3.33. This is why comparing ROAS across businesses without margins is misleading.
How do you calculate CAC?
Formula: CAC = Total acquisition costs / Number of new customers
Shopify’s guide recommends including more than ad spend: marketing software, marketing salaries, discounts used for acquisition, content production and agency fees. Decide what you include once and keep it consistent month to month.
Example: In one month, the brand spends ₹2,50,000 on ads and ₹50,000 on agency fees, tools and content, a total of ₹3,00,000. It acquires 400 new customers.
Blended CAC = 3,00,000 / 400 = ₹750.
CAC versus CPA
Cost per acquisition (CPA) in an ad platform is spend divided by conversions, which usually includes repeat customers. CAC counts only new customers. If 150 purchases came from a campaign but only 100 were first-time buyers, the CPA on ₹1,00,000 is ₹667 while the new customer cost is ₹1,000.
CAC needs lifetime value next to it
CAC alone does not tell you whether a customer is worth acquiring. Compare it with contribution lifetime value (LTV): the total contribution a customer generates over a set period, such as 12 months.
Example: Customers place 1.8 orders on average in their first 12 months. Contribution LTV = 1.8 × ₹900 = ₹1,620.
LTV to CAC ratio = 1,620 / 750 = 2.16.
First-order profit after CAC = 900 minus 750 = ₹150, so this customer pays back on the first order.
Shopify’s guide suggests that an LTV to CAC ratio between 3:1 and 5:1 indicates an efficient acquisition strategy. Our example brand is profitable on the first order, but at 2.16 it has limited room to raise CAC to grow faster unless repeat purchase improves.
How do you calculate MER?
Formula: MER = Total revenue / Total marketing spend
MER, sometimes called blended ROAS, ignores which platform claims the sale. It uses total revenue from your store or finance system and total marketing spend across all channels. HubSpot’s MER guide uses the same formula and describes MER as a measure of overall marketing effectiveness across channels.
Example: Total store revenue for the month is ₹12,00,000, including organic, email, repeat and paid orders. Total marketing spend is ₹3,00,000.
MER = 12,00,000 / 3,00,000 = 4.0.
One caution: some tools flip the formula. Triple Whale, for example, presents MER as spend divided by revenue, shown as a percentage. In that version, our example would be 25%. Agree on one definition inside your team.
Break-even MER
The break-even logic also works at business level. If your blended contribution margin is 45%, a blended MER below 2.22 means marketing is costing more than the contribution it brings in. Most brands need MER well above break-even to cover fixed costs and still make a profit.
Which metric should you optimise for?
Each metric answers a different question, so the right one depends on the decision you are making.
| Decision | Primary metric | Guardrail |
|---|---|---|
| Which ad, ad set or campaign to scale | Platform ROAS or CPA | Must stay above break-even ROAS |
| Setting a Target ROAS or ROAS goal in Google or Meta | Break-even ROAS plus a profit buffer | Watch volume; very high targets limit reach |
| How much to spend on marketing in total | MER | Contribution profit after marketing |
| Whether to push for faster customer growth | New customer CAC | LTV to CAC ratio and payback period |
| Comparing channels against each other | Incremental results from holdout or geo tests | MER movement when spend changes |
A simple rule for most D2C brands
- Early stage, low repeat purchase: optimise for first-order profit. Keep campaign ROAS above break-even and MER comfortably above it.
- Growth stage with proven repeat purchase: you can accept a ROAS closer to break-even on new customer campaigns, because LTV covers the gap. Track CAC payback in months.
- Mature stage: manage to a target MER and a contribution profit figure, and use platform ROAS only to allocate budget within channels.
Checklist: setting up these metrics correctly
- Calculate contribution margin per order with real costs, including shipping, payment fees and returns.
- Work out break-even ROAS and share it with everyone who manages campaigns.
- Set ROAS targets in ad platforms above break-even, with a buffer for profit.
- Pull total revenue from your store or accounts, not from ad platforms, for MER.
- Separate new customers from returning customers when calculating CAC.
- Agree one definition for each metric and document it.
- Review MER and CAC monthly, and campaign ROAS weekly.
If your site’s checkout or tracking is unreliable, every number above is affected. Clean conversion tracking on your Shopify store is the first fix before any optimisation.
How Squarebase can help
Squarebase sets up margin-based targets, tracking and reporting so that ad decisions are tied to profit, not only platform ROAS. See our performance marketing services or contact us to review your numbers.
Frequently asked questions
What is the formula for ROAS?
ROAS equals revenue attributed to ads divided by ad spend. If a campaign spends ₹1,00,000 and generates ₹3,00,000 in attributed revenue, ROAS is 3.0, also written as 3x or 300%. Google Ads shows Target ROAS as a percentage.
How do I calculate break-even ROAS?
Break-even ROAS equals 1 divided by your contribution margin percentage. Contribution margin is revenue minus product cost and variable costs such as shipping, packaging, payment fees and returns. With a 45% contribution margin, break-even ROAS is 1 / 0.45, or about 2.22.
What is the difference between ROAS and MER?
ROAS measures revenue attributed to a specific campaign or channel divided by its ad spend. MER divides total business revenue by total marketing spend across all channels. MER does not depend on platform attribution, so it is better for judging overall marketing efficiency.
What should be included in CAC?
CAC should include all costs of acquiring new customers in a period: ad spend, agency fees, marketing tools, content production, acquisition discounts and relevant marketing salaries. Divide that total by the number of new customers only, not repeat buyers, in the same period.
Should I optimise for ROAS or CAC?
Use ROAS to manage campaigns, keeping it above your break-even ROAS. Use CAC, compared with customer lifetime value and payback period, to decide how aggressively to grow. Use MER to set total marketing budget. Each answers a different decision, so track all three.
