Determine how many impressions to book

The number of impressions you can book depends on how willing you are to displace or preempt existing inventory.

First, run a forecast for the prospective line item. Remember that your line item's trafficking criteria can greatly affect the number of available impressions.

How forecasting accounts for trafficking criteria

Forecasting takes most trafficking criteria into account when determining available inventory, but there are some details you should keep in mind:

Frequency capping

Frequency capping is considered. Because DoubleClick for Publishers uses a 28-day sample, monthly or lifetime frequency caps are not captured as part of the sample data. Consequently, in cases with monthly and lifetime frequency caps, forecasting can overpredict availability.


Forecasting looks at priority to determine the Reserved for lower-priority line items number--the number of impressions a line item can get if you’re willing to take impressions from lower priority line items. Priority is also taken into account when calculating impressions likely to deliver.

Deliver impressions (evenly, frontloaded, as fast as possible)

Forecasting ignores this delivery control. Instead, it optimizes delivery the best it can. For example, if a line item is set to deliver evenly, the forecast simulation might allocate impressions on a frontloaded basis. In some cases, this can lead to overly optimistic forecasts.


Cost is not a criteria considered in forecasts.

Roadblock ads

When you run a forecast on roadblock ads, DoubleClick for Publishers projects available inventory for all creative sizes in the line item, regardless of whether or not they serve together in a single view.

For example, if you have a line item containing one creative that’s 728x90 and one that’s 300x250, for three page views, forecast results count one impression for a view in which just the 728x90 creative is projected to serve, one for when just the 300x250 is projected to serve, and two for when they’re projected to serve together (the roadblock). The forecasting simulation returns a result of four, which accurately simulates how this line item would serve when live, even though there is only one page in which both the 728x90 and the 300x250 would serve together to the same page.

Multiple creatives of the same size

If you have an ad with multiple creatives of the same size, and you select the “As many as possible” setting for displaying creatives, then forecasting can underestimate the available inventory because it currently assumes every ad has only one creative of a given size. For example, if you have an ad that has two 300x250 creatives, and a webpage with two ad slots of that size, the forecast simulation counts one page view as one impression, whereas in reality, both creatives will serve, making two impressions. So in this case you should double the number of available impressions to get an accurate count of how many impressions to safely book.

Example: forecasts on line items with multiple creatives of the same size

The table below details expected forecast results based on the following assumptions:

  • The website has three pages in the following configuration:

    • Page one has 3 slots of 300x250

    • Page two has 2 slots 728x90

    • Page three has 2 slots of 300x250 and 1 slot of 728x90

  • Line item delivery is set to "As many as possible."

Creative size(s) No. of creatives Forecast imps Actual imps
300x250 1 2 2
300x250 2 2 4
300x250 3 2 5
300x250, 728x90 1, 1 4 4
300x250, 728x90 2, 2 2+2=4 4+3=7
300x250, 728x90 3, 2 2+2=4 5+3=8


Forecasting results

Results on the first page of the forecast provide guidance that can help you decide how many impressions to book.

  • Available: These are impressions that match the line item’s targeting criteria and are currently unencumbered by obligations to other line items of any priority. Booking this number won't take impressions from other line items.

  • Reserved for lower-priority line items: These are impressions that can be safely displaced from line items at the same priority as the current line item or taken away from lower-priority line items. Doing so might negatively affect the delivery of these line items.

  • Unavailable: Impressions or clicks might be unavailable to this line item for the following reasons:
    • They're reserved for higher-priority line items.

    • They're reserved for same-priority line items that can't be displaced to other available inventory.

    • Restrictions apply, such as frequency capping for the prospective line item, competitive exclusions, ad exclusion labels, max creatives per page, roadblocking, and possibly others.
  • Matched for specified targeting criteria: The sum of "Available," "Reserved for lower-priority," and "Unavailable." This is the total number of impressions that would be available to the line item if it were unencumbered by other line items and any delivery restrictions, such as frequency capping.

You can also gauge and adjust the effect that booking the prospective line item would have on existing line items by clicking the View contending line items link. (Learn more)