How a CDP's Cost Crept Up 4x Without Anyone Noticing

The client's finance team flagged it as a line-item review: the CDP bill had gone from roughly $2,400 a month to over $9,600 over eighteen months, with no corresponding decision anyone could point to that explained the jump. Nobody had signed off on a 4x increase. It had just happened, a little at a time, invisibly, inside a billing model based on event volume that nobody was actively watching.

Where the volume actually came from

We pulled the event logs and found the growth wasn't from legitimate new tracking needs — it was from a slow accumulation of redundant and low-value events. A page-view event was being sent twice due to a duplicated snippet from an old site migration nobody had cleaned up. A debug event meant to be temporary during a feature launch eight months earlier had never been removed. And three new product teams had each independently started sending granular interaction events without checking what was already being tracked or what the CDP's pricing model actually charged for.

Nobody approved a 4x cost increase. Four separate small decisions, each individually reasonable, approved it by accident.

The actual breakdown

• Duplicated page-view events from an old migration: roughly 30% of the excess volume.
• An abandoned debug event firing on every session: roughly 20%.
• Three product teams' independently added granular interaction events: roughly 35%.
• Genuine organic growth in legitimate tracking needs: the remaining 15%, the only part that was actually a reasonable cost increase.

What fixed it going forward

We cut the duplicate and abandoned events immediately, bringing the bill down by more than half in the next cycle. The longer-term fix was process, not cleanup: a lightweight approval step for any new event type going into the CDP, and a monthly volume-by-source report that gets reviewed by someone with the context to notice when a number looks wrong. The tooling was never the problem. The absence of anyone watching the meter was.