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How ad selection works

Applies to: Advertisers

Every time a page loads an ad zone, the ad server decides in a few milliseconds which ad to show. This explains that decision, so you can see why a campaign wins an impression — or doesn't. There's nothing to set up here.

The order#

The ad server works down a fixed list and stops at the first step that produces an ad:

  1. Direct deals. If the ad zone has a direct deal that matches this visitor, the deal serves and nothing else is considered. Between several deals, Exclusive wins, then Percentage Based (for its share of the traffic), then the capped types, then Remnant. See How to set up a direct deal.
  2. SmartZones. If the publisher has turned the zone into a SmartZone, the SmartZone picks one of its connected ad networks' codes. See Smart Zones.
  3. Campaigns (RON and targeted). All eligible campaigns compete on expected earnings — see the next section.
  4. Fallback. If no campaign qualifies, the zone shows its fallback: the publisher's own ads or a failover campaign, so the space is never empty when one is set.

RTB on top. On zones that use RTB, once an ad has been chosen in step 3, connected bidders get a bid request with that ad's price as the floor. A higher bid replaces the ad. Zones with campaigns assigned to them directly, and direct deals, skip this. See How to buy traffic with your own bidder.

How campaigns compete#

Before the competition, every campaign that can't serve is removed:

  • Wrong format or size — the ad type and ad size must fit the zone.
  • Zone assignment — if the zone only runs the campaigns assigned to it, all other campaigns are left out.
  • Targeting — country, device, operating system, browser, language, connection, schedule, keywords and your include/exclude lists. See Targeting & Filters.
  • Budget — a campaign that has spent its daily or total budget, or an account without funds, sits out.
  • Frequency capping — an ad this visitor has already seen as often as allowed sits out for them.

The remaining ads are ranked by eCPM — what the ad is expected to earn per thousand impressions:

Payment type How its eCPM is worked out
CPM Your CPM bid
CPC What the ad has actually earned per thousand impressions on this zone — in effect your CPC bid × its click-through rate there
CPA (and CPL, CPI, CPS) What the ad has actually earned per thousand impressions on this zone — in effect your payout × its conversion rate there

The highest eCPM wins. A new CPC or CPA ad with no history on a zone starts from an estimate (its bid and the zone's typical click-through rate, reduced at first) that moves to its real value as it collects views, so new ads get a fair trial without pushing out proven ones.

Example#

A banner zone in Germany gets a visit from an Android phone. It has no direct deal and isn't a SmartZone. Three campaigns target Germany:

  • A bids a CPM of 2.00 → eCPM 2.00.
  • B bids a CPC of 0.20 with a 1.5% click-through rate on this zone → 0.20 × 0.015 × 1000 = eCPM 3.00.
  • C bids a CPM of 4.00 but only targets desktop → removed before ranking.

B wins, even though A bids "more" per view on paper. If the zone uses RTB, a bidder now gets the chance to beat 3.00.

Tips#

  • On CPC and CPA, your creative counts as much as your bid. Doubling your click-through rate has the same effect as doubling your bid.
  • Check your targeting before raising the bid. A campaign removed by targeting or budget loses every time, whatever it bids.

Troubleshooting#

Symptom Likely cause Fix
My campaign gets no impressions on a zone A direct deal or SmartZone serves there, or the zone only runs assigned campaigns Ask the publisher or your account manager
Few impressions despite a high CPC bid Low click-through rate makes the eCPM low Improve the creative, or switch to CPM
Impressions stop every afternoon The daily budget runs out Raise the daily budget or turn on budget spreading
A new ad barely serves at first It's still in its trial phase on that zone Give it a few days of traffic