Reading · Measurement

Why you should stop optimising to platform ROAS (and what to use instead)

5 min read

Platform ROAS, the number Meta or Google reports, counts conversions each platform takes credit for, often double-counting and over-attributing. Optimising to it makes you scale back the channels that actually drive incremental sales. Instead, anchor on blended MER, total revenue divided by total ad spend, and new-customer CAC against LTV, and use incrementality tests to see what truly moved the needle.

The double-counting problem

If Meta and Google both claim the same sale, your combined reported ROAS can exceed reality. Founders who trust it end up over-crediting retargeting and starving prospecting.

Blended MER is the honest number

Total revenue over total spend, read at the account or business level, cannot be double-counted. Track it weekly and watch the trend as you scale.

Prove incrementality

Geo holdouts, spend-down tests and conversion-lift studies show what sales you would have lost without the spend. That is the number worth optimising to.