CPM (Cost Per Mille)

What is CPM?

CPM is the cost to serve 1,000 ad impressions (ad spend ÷ impressions, times 1,000), and it is a read on auction competition, audience value, and creative quality rather than a bid you force down.

The formula and a worked example

CPM = (ad spend ÷ impressions) × 1,000. Work an example with round, illustrative numbers. An ad set spends $1,300 and serves 100,000 impressions, so CPM is ($1,300 ÷ 100,000) × 1,000 = $13. Hold the audience steady but let the creative fatigue, and the platform charges more to keep forcing a tired ad into the same feeds, so the same 100,000 impressions might cost $2,200 (a $22 CPM) with nothing about the audience having changed.

What CPM is actually telling you

Three forces move CPM, and separating them is the whole skill. Auction competition sets a floor: more advertisers bidding for the same eyeballs, as in Q4 and around open enrollment, lifts everyone’s CPM at once. Audience value raises it further, since a high-intent, high-value segment costs more to reach than a broad one. And creative quality pulls it back down, because the platform rewards ads people stop for with cheaper delivery. That last lever is the one you control, which is why a rising CPM on a stable audience is usually a creative signal, not an auction one.

Why it matters for health and DTC brands

Health CPMs run higher than most because the auctions are restricted and the audiences are valuable: industry benchmark data puts health and medical Meta CPMs around $13 and supplement CPMs higher near $18, both inflating year over year. That makes CPM the earliest place creative fatigue shows up, ahead of ROAS: across AdBoost Health partner accounts, a GLP-1 account whose CPM climbs from $14 to $22 on a stable audience is watching its creative stop earning delivery, and the fix is fresh angles at the standard 15–25 variants per month, not a lower bid. Read CPM next to hook rate to confirm fatigue (a falling hook rate on rising CPM is the tell) and next to CPC to separate the cost of reach from the cost of a click. Because CPM is a symptom to interpret rather than a dial to force, monitor it against your own trailing baseline so a rotation still fixes the problem cheaply, and keep the pipeline feeding creative testing ahead of the decay.

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