Scaling budget without watching CPM is the #1 reason ROAS collapses at scale

Scaling budget without watching CPM is the #1 reason ROAS collapses at scale

CPM (cost per 1,000 impressions) rises as you push budget into a fixed audience — you climb the auction supply curve.

CPM vs daily budget, same ad set (32 accounts):
— $100/day: $14 CPM (baseline)
— $500/day: $19 CPM (▲36%)
— $2,000/day: $27 CPM (▲93%)

ROAS dies not because creative broke, but because each sale now costs 2× the impressions.

Fix: when scaling, watch CPM as your early-warning gauge. If CPM climbs >30% above baseline, you've saturated — expand the audience (new geo, broader age) or add fresh creative before adding budget.

Read: at scale you're not buying conversions, you're renting attention — and the rent goes up every dollar.