WordPressA CPM change means the same reach now costs more or less than before. It is a price signal, not a verdict on the ads, so find the cause before you act on it.
Check in this order
- First, the setup. Did a budget, bid strategy, audience or placement change? Check the change log for the same days.
- Second, the mix. A bigger share of impressions from a dearer placement, device or country moves the blended CPM, even when each part is steady.
- Third, the audience. A narrow audience shown many times gets dearer, and frequency rises with it. Read frequency next to CPM.
- Fourth, the season. Compare with the same weeks last year before you call the change new.
What a CPM change does not prove
- It does not prove the ads work. A cheaper impression can bring fewer sales.
- A higher CPM can still be the better buy if sales per impression are higher too.
Writing it up
- Write the cause, the number before and after, and whether the change was expected.
Made-up scenario: CPM rose from 9.00 to 13.00 in one week. The change log showed a new broad audience added on Monday, and the placement mix was unchanged. Frequency was flat. The team kept the audience, read cost per purchase for a week, and logged the outcome.
