MER Calculator

The MER formula, and why it holds up

MER = total revenue ÷ total ad spend

That is the whole model. All revenue from every source, all paid media from every platform, one division. No attribution windows, no modeled conversions, no platform claiming an order another platform also claimed. If the money landed in the account and the spend left it, MER counts it. That is why people call it bank-account math: you can verify it from your P&L in two minutes, and nobody can argue with it in a meeting.

MER vs platform ROAS

Platform ROAS answers "what does Meta think Meta drove". MER answers "what did the business get back for everything we spent". On brand-heavy accounts the gap is enormous. I manage accounts where platform ROAS runs 2 to 19 times above what the blended numbers support. When the two disagree, believe the bank account.

The trap MER hides

Because MER blends everything, it also hides everything. A business with strong brand demand from TV, retail or word of mouth can show a beautiful MER while its paid channels quietly do nothing. Revenue that would have arrived anyway props up the ratio. So use MER for totals and planning, but pair it with incrementality checks before crediting the ads: holdout tests, geo splits, or simply pausing a channel for two weeks and watching what actually changes.

The inflation factor

inflation factor = Σ platform-reported revenue ÷ actual revenue

Add up what every ad platform claims it drove and divide by what you actually made. Above 1.0 the platforms are collectively reporting revenue that does not exist, which is common: each attribution model claims the same order, and none of them subtracts the customers who would have bought anyway. Even below 1.0, a combined claim near your total revenue deserves suspicion on any brand that gets meaningful organic, email or repeat business. This single number is often the quickest way to show a founder why the platform dashboards and the bank account tell different stories.

Planning with the spend ceiling

spend ceiling = revenue ÷ target MER

Pick the MER your margins need, divide expected revenue by it, and you have the most you should spend this month. The headroom readout is that ceiling minus what you already spend. Positive headroom means room to test new channels or push winners. Negative headroom means you are buying revenue at a worse rate than your target allows, and the first move is usually cutting the weakest campaign, not quietly lowering the target until the number turns green.