ADSSystem

MER and blended ROAS calculator

Total revenue against total marketing spend, next to what the platforms claim they produced.
In one line

Divides all revenue by all marketing spend, then shows the break-even MER your margin requires and how much revenue the ad platforms are claiming twice.

MER = Total revenue / Total marketing spend
$
Everything the business took in the period, not just paid channels.
$
Every channel, plus agency and tool costs.
$
Add up what each ad platform claims it drove.
MER, or blended ROAS-
Break-even MER-
TACOS, spend over revenue-
Revenue the platforms claim-
Contribution after marketing-
Where $180,000 of revenue goes42% gross marginActual, MER 4.29$104,400$42,000$33,600Break-even, MER 2.38$104,400$75,600 of marketing, nothing leftCost of goodsMarketing spendContribution after marketing

The formula

MER = Total revenue / Total marketing spend

Every dollar in, every dollar out, no attribution involved. That is the whole point. MER cannot be inflated by a platform claiming credit, because it never asks any platform what it did.

Break-even MER is one divided by gross margin. At a 42 percent margin you need 2.38 to stand still, so a MER of 4.29 means marketing is funding fixed costs as well as covering goods.

MER, blended ROAS and TACOS are one number in three costumes

  • MER is total revenue over total marketing spend. Ecommerce teams say this.
  • Blended ROAS is the same division, usually said by agencies to distinguish it from platform ROAS.
  • TACOS is the reciprocal expressed as a percentage, spend over revenue. Amazon sellers say this.

A MER of 4.0 is a blended ROAS of 4.0 and a TACOS of 25 percent. Arguing about which to report is a vocabulary problem, not a measurement one.

When platform ROAS and MER disagree

Platform ROAS is almost always the higher number, and the gap has a few ordinary causes worth separating before anyone blames the media buyer.

  • Two platforms claiming the same order, so reported revenue sums above actual revenue.
  • View-through windows counting people who would have bought anyway.
  • Revenue arriving through channels that report nothing, which drags MER down while platform ROAS stays flat.
  • Returns, which hit the bank account but rarely the ad dashboard.

If reported revenue exceeds total revenue, the arithmetic has already told you the platforms are double counting. No attribution model is needed to see it.

The trap

MER is honest about the total and silent about the parts.

Because MER ignores attribution, it also ignores allocation. A healthy MER can hide a channel burning money, offset by organic revenue that would have arrived regardless. Scaling on MER alone tends to scale the wrong channel.

Use MER as the ceiling that decides how much total spend the business can carry, and use incrementality tests or geo holdouts to decide where that spend goes. One number cannot do both jobs.

Frequently asked

There is no universal number. Break-even MER is one divided by gross margin, so a 40 percent margin needs 2.5 to stand still. A good MER sits far enough above break-even to cover fixed costs and leave profit.
ROAS is per platform and uses attributed revenue. MER uses all revenue and all spend, including channels that report nothing, so it cannot be inflated by attribution.
Yes. Same arithmetic, different word. TACOS is the same relationship inverted and shown as a percentage.
If the aim is to know what marketing costs the business, yes. Media-only MER is useful for comparing periods, but it flatters the number by leaving out the people who spend the media.