By Ashish Rai, CEO, Purple Circle · Updated August 2026 · 8 min read

Three dashboards can all report a profitable month while your bank balance goes down.

That is not a tracking bug. It is what happens when you run a business on a metric that was built to grade an ad account.

Most founders know the definitions of ROAS and MER. Very few have laid them side by side on their own numbers and watched the gap. That gap is the entire article.

What each metric is actually measuring

Forget the textbook version. Here is what each number is really doing.

Platform ROAS answers: how much revenue does this platform believe it caused?

The key word is believe. Meta, Google, and TikTok each run their own attribution model on their own data. None of them can see each other. None of them can see your product cost.

Blended ROAS answers: total revenue divided by total ad spend.

Better, because it uses one revenue number instead of three competing claims. Still blind to what it costs you to fulfil the order.

MER (Marketing Efficiency Ratio) is the same arithmetic as blended ROAS, but it is a business metric rather than a channel one. Total revenue divided by total marketing spend across everything — ads, agency fees, influencer payments, creative production.

Contribution MER (sometimes aMER) answers: how much gross profit came back for every dollar of marketing?

This is the one that tracks the bank. Contribution margin divided by total marketing spend. It knows your COGS, your shipping, your discounts, and your returns.

Four metrics, one business, four very different answers. Here is what that looks like with real arithmetic.

One store, six numbers

Take a US apparel brand doing $300,000 a month in Shopify gross sales. All figures in USD. These are illustrative numbers, not a client account, but every input sits inside the range that is normal for US apparel.

Ad spend for the month: $100,000

• Meta: $68,000
• Google: $24,000
• TikTok: $8,000

What the platforms report:

The three platforms claim $348,800 in revenue. The store made $300,000.

They have claimed $48,800 of revenue that does not exist. Not because anyone is cheating — because the same order gets claimed by more than one platform. Someone sees a Meta ad on Tuesday, searches your brand name on Thursday, clicks a Google ad, and buys. Meta counts it. Google counts it. You banked it once.

Number 1: Meta ROAS — 3.4

This is the number in the weekly agency report. It is a channel diagnostic. It is useful for comparing this week’s Meta performance to last week’s Meta performance, and for almost nothing else.

Number 2: Blended platform ROAS — 3.49

Adding up what the platforms claim and dividing by spend. This number is worse than useless because it bakes the double-counting straight in. If anyone reports this to you, it is a red flag.

Number 3: MER on gross revenue — 3.0

$300,000 ÷ $100,000 = 3.0

Now we are using the store’s own revenue instead of the platforms’ claims. Real progress. This is the number most brands settle on.

But Shopify gross sales includes orders that get refunded later.

Number 4: MER on net revenue — 2.34

At a 22% return rate, 880 of the 4,000 orders come back. At a $75 average order value that is $66,000 of revenue that leaves again.

$300,000 − $66,000 = $234,000 net revenue.

$234,000 ÷ $100,000 = 2.34 MER

One caveat on timing: the refunds landing this month mostly belong to orders placed 30 to 45 days ago. Run this on a rolling three-month window rather than a single month, or you will chase noise.

Your 3.0 just became 2.34, and nothing about your advertising changed.

Number 5: Contribution MER before returns — 1.34

Now we account for what it costs to actually deliver an order.

Per order, at a $75 AOV:

4,000 orders × $33.52 = $134,080 of contribution margin.

$134,080 ÷ $100,000 = 1.34 contribution MER

For every dollar spent on marketing, $1.34 of gross profit came back. Thin, but positive.

Number 6: Contribution MER after returns — 0.80

This is where it breaks.

A returned order does not simply cancel out. The ad spend that acquired it is gone. The outbound shipping is gone. And you now pay again to bring it back.

Per returned order:

Now run it across the month:

• 3,120 kept orders × $33.52 = $104,582
• 880 returned orders × −$28.48 = −$25,062
• Net contribution margin: $79,520

$79,520 ÷ $100,000 = 0.80 contribution MER

You spent $100,000 on marketing and $79,520 of gross profit came back.

That is a loss of $20,480 for the month, before rent, salaries, software, 3PL storage, or your own pay.

The ladder

Same store. Same month. Every number in that table is arithmetically correct.

The one at the top is what gets reported. The one at the bottom is what shows up in the bank.

Why platform ROAS runs high — the technical part

It helps to know the mechanisms, because they tell you which numbers to distrust and by roughly how much.

Attribution windows. Meta’s default is 7-day click, 1-day view. A view-through conversion means someone saw your ad, did not click, and bought within 24 hours. Meta claims that order. So does the email that actually drove it. Check your window setting before you compare any two periods — a lot of “performance improvements” are window changes.

Modeled conversions. After iOS 14.5 and ATT, a meaningful share of iOS conversions are not observed, they are estimated statistically and then reported as though they were counted. The estimate is not random, but it is an estimate, and it is not conservative.

Cross-channel double counting. This is the big one, and it gets worse as you add channels. Branded search is the usual culprit: Meta creates the demand, Google captures it, and both invoice you for the same customer.

Pixel and CAPI deduplication. If you run the browser pixel and the Conversions API without a matching event_id on both, the same purchase gets counted twice on the same platform. Worth 15 minutes with your developer to verify. In Events Manager, check the deduplication rate on your Purchase event — it should be showing matched events, not two separate streams.

Sales tax. In the US you collect it, you do not earn it. Shopify’s total sales figure includes sales tax and shipping revenue. If you calculate MER on total sales, you are counting the state of Texas’s money as your own.

Gross vs net vs total sales in Shopify. These are three different numbers in your reports and people use them interchangeably. Gross sales excludes discounts and returns. Net sales includes discounts, excludes returns. Total sales includes shipping and tax. Pick one and use it everywhere. Net sales is the right default for MER.

GA4 will not match either. GA4 uses last non-direct click by default. Meta uses its own model. They are answering different questions and will never reconcile. Do not spend a week trying.

The practical rule: any revenue figure that comes from an ad platform is a claim. Any revenue figure that comes from Shopify payouts or your bank is a fact. Build your reporting on the second kind.

So what do you actually do with this

Run the ladder on your own store once. Not weekly. Once, properly, in a spreadsheet, on a rolling 90-day window so returns line up with the orders that produced them. You need six columns: gross revenue, refunds, COGS, shipping and fulfillment, processing and discounts, total marketing spend. Most of it comes out of Shopify’s finance reports in about an hour.

Then set your breakeven contribution MER. In the example above, contribution after returns is 26.5% of gross revenue. To break even on ads alone the store needs a gross MER of about 3.8. It is running at 3.0. That is the actual gap — not “improve ROAS,” but a specific number with a specific distance to it.

And here is the part most people miss. Look at what happens when you fix operations instead of the ad account:

Both together moves the store from losing $20,480 a month to making $10,150. A swing of roughly $30,000, with zero change to media buying.

No amount of campaign restructuring produces that. The ad account was never the constraint.

Which metric to use, and when

• Platform ROAS — for comparing one channel to itself, week over week. Creative testing, campaign diagnostics. Never for business decisions.
• MER — for the weekly leadership number. Is the machine getting more or less efficient at turning marketing dollars into revenue?
• Contribution MER after returns — for the decisions that matter. Can we scale? Can we afford this hire? Should we take this inventory position?

Run the business on the third one. Report the second one. Let your media buyer worry about the first one.

If your agency only ever shows you the first one, that is worth a conversation. Not because they are dishonest — most are not — but because a report that cannot go negative is not telling you anything you can act on.

Frequently asked questions

What is the difference between ROAS and MER?

ROAS is reported by an ad platform and measures the revenue that platform believes it caused. MER is total revenue divided by total marketing spend across all channels, calculated from your own store data. ROAS is a channel diagnostic. MER is a business metric.

What is a good MER for an ecommerce brand?

There is no universal figure. A healthy scaling store often sits between 3 and 5, but the correct target depends on your own contribution margin. Divide contribution margin after returns by gross revenue, then take one divided by that percentage. That is your breakeven MER.

Why is my ROAS good but my store not profitable?

ROAS knows nothing about product cost, shipping, discounts, payment processing or returns. A store can report 3.4 ROAS on Meta while contribution margin after returns comes to less than the marketing spend that produced it.

What is contribution MER?

Contribution MER, sometimes called aMER, is contribution margin divided by total marketing spend. Unlike MER it accounts for cost of goods, fulfillment, discounts and returns, which makes it the closest metric to actual cash movement.

Ashish Rai — CEO, Purple Circle

Ashish has spent over eight years in ecommerce, working with D2C brands on the side of the business most agencies never open: contribution margin, cash cycle, and what actually reaches the bank. Purple Circle is a performance marketing agency built around profit rather than reported ROAS.

At Purple Circle we calculate contribution MER after returns before we look at a single campaign. If your dashboards look healthy and your bank account does not, that number is usually where the answer is.