Can the average CPM per line exceed the “Maximum average CPM per line”?
- The planned budget has not been spent in its entirety yet (under the “Budget” and “Average CPM” strategies) or all the planned impressions have not been served yet (under the “Minimum CPM” strategy).
Under the “Budget” strategy, the planned budget is 100,000 RUB with a maximum average CPM of 100 RUB. The current budget expenditure is 3,000 RUB, which was used to purchase 25,000 impressions. If the current average CPM is calculated, it will equal 3,000/25 = 120 RUB.
This is because the actual CPM in this scenario is only calculated for part of the line period, whereas the limit applies to the entire period.
- During the course of a line, the planned budget or number of impressions was adjusted down or the end date was pushed up. Before that change was made, the average CPM exceeded the limit (see situation #1). As a result, the algorithm can't keep the CPM under the stated maximum in the short time that remains.
Under the “Budget” strategy, the planned budget is 100,000 RUB with a maximum average CPM of 100 RUB. The current budget expenditure is 3,000 RUB, which was used to purchase 25,000 impressions. Therefore, the current average CPM is 3000/25 = 120 RUB. Then let's say the planned budget was cut to 6100 RUB. With the remaining budget (6 100 — 3 000 = 3100 RUB.), 31,000 impressions were purchased (3 100/100 = 31 К). The CPM limit of 100 RUB was thus observed. However, because major changes were made to the plan during the course of the line, the final CPM will still exceed the maximum average CPM.
- The maximum average CPM was lowered significantly over the course of the line. To stay within the new limit, bids decreased significantly and impressions were served at a slower rate because competitors did not allow impressions to be purchased at such a low rate at auction. As a result, the number of impressions served is so low that the average CPM will exceed the (recently lowered) maximum CPM.
The “maximum average CPM for a line” is 120 RUB and 90% of the line was fulfilled with an actual average CPM of 100 RUB. Then let's say the maximum average CPM was lowered to 50 RUB. In this case, even if all remaining impressions are served for one ruble apiece, the average CPM will be 0.9*100 + 0.1*1 = 90.1 RUB (which exceeds the 50 RUB maximum average CPM).