A price floor is the lowest price a seller will accept for an advertising impression sold at auction. Bids beneath it are discarded before any winner is chosen. Usually quoted as a cost per thousand impressions (CPM), it exists because an auction with few bidders can clear far below what inventory is worth, and because publishers selling directly to advertisers need automated demand not to undercut those deals. Auction theorists say reserve price; the Media Rating Council (MRC) treats the terms as synonyms.

How a floor travels through an auction

A publisher's ad server, supply-side platform (SSP) or header bidding wrapper, the page code gathering exchange bids before the ad server decides, matches each ad request to a rule by placement, size, format or country, then writes the number into the bid request sent to demand-side platforms (DSPs), the systems advertisers buy through.

OpenRTB, the IAB Tech Lab protocol carrying most such requests, gives the value a fixed home. The impression object holds bidfloor, a float defaulting to 0 and expressed in CPM, and bidfloorcur, a currency code defaulting to US dollars. A private marketplace deal can carry its own bidfloor, which does not inherit the impression's currency. Video and audio add duration-based forms: mincpmpersec, a minimum per second of creative, and durfloors, an array pricing duration bands separately. The specification's illustration sets $5 for creatives of one to 15 seconds, $10 for 16 to 30 seconds and $20 above 31.

Bids below the threshold are dropped. The loss reason codes OpenRTB references reserve 100 for a bid below the auction floor and 101 for one below a deal floor, and the AUCTION_MIN_TO_WIN macro returns the floor itself to a winner that faced no rival.

A worked example from Yahoo researchers shows why the auction rule matters. Two DSPs value an impression at $1 and $3. In a second price auction with a $0.50 floor, the $3 bidder wins and pays $1. Raise the floor to $2.50 and the same winner pays $2.50: the floor, not the rival, sets the price. Under first price, where winners pay their own bid, a $2.50 floor facing bids of $1 and $2 produces no sale unless the stronger buyer lifts its offer.

Configuration in practice

Google Ad Manager centralises floors in pricing rules, capped at 200 per network according to its help centre as of September 2026. Each rule takes a fixed floor, a target CPM, the default, under which Google moves the floor per request while aiming to hold the average, or a beta option letting Google's models set floors per query. Floors are measured after Google's revenue share: under an 80/20 split a $1.00 bid is worth $0.80 to the publisher and is filtered by any floor above that.

Buyers may not see the figure enforced: bidfloor carries only the level below which a bid is certain to be filtered, while floors for specific advertisers, brands or sizes apply undisclosed.

Prebid.js, the open-source wrapper, handles floors through its Price Floors Module, proposed on GitHub in October 2019. Rules key on ad unit, slot, media type, size and domain, and can be fetched from a vendor endpoint before the auction. A skipRate from 0 to 100 switches floors off for a random share of auctions to measure their effect, floorMin bounds algorithmic values from below, and deal bids are exempt by default. Prebid's documentation discourages static floors as blunt, and lists six floor providers including Magnite, OpenX and PubMatic. In apps, AdMob added bidding eCPM floors at mediation group level in July 2025.

Origin and evolution

The theory is older than online advertising. Roger Myerson, and separately John Riley and William Samuelson, showed in 1981 that with symmetric bidders a revenue-maximising auction can be run as an ordinary first or second price auction with a well-chosen reserve. Jeremy Bulow and Paul Klemperer countered in 1996 that, in single-item auctions, attracting one more bidder beats setting the optimal reserve.

Search advertising supplied the first large test. The sponsored search business Yahoo later operated set a reserve of 1 cent per click in 1998, raised it to 5 cents in 2001 and to 10 cents in 2003, according to Michael Ostrovsky and Michael Schwarz. In mid-2008 Yahoo tested keyword-specific reserves on 461,187 keywords. The results, published in December 2023, were uneven: nearly one fewer ad appeared per results page, and revenue per search rose 3.9% on frequently searched keywords but fell 8.7% on busy keywords whose estimated optimal reserve was below 20 cents.

Exchanges carried the concept into display. OpenRTB 2.0, released for comment on June 30, 2011, already included bidfloor and bidfloorcur. Version 2.2, dated April 2014, added a floor to the direct deal object; version 2.6 introduced mincpmpersec in 2022, and a July 2023 update added durfloors.

The second price era taught sellers to use floors as a pricing lever. Announcing on May 10, 2019 how Ad Manager would move to first price, Google said publishers had raised floors to lift second-price closing prices, eroding trust in the format. Its existing floor rules were discontinued with the switch and replaced by unified pricing rules, which Jason Bigler, then a director of product management, said would be "applied to all partners equally, and cannot be set for individual buying platforms". The beta allowed 100 rules per network, a limit Google raised by September 2019 after publisher objections.

Automation followed. Yahoo began setting daily model-driven floors by placement on North American display inventory in June 2021, and its researchers estimated annualised revenue gains of 1.3% on display and 2.5% on video.

Why floors matter to buyers and sellers

For a publisher, the floor is the main price instrument left in an open auction, and it trades volume for price. In Yahoo's third quarter 2022 figures, impressions cleared through its exchange fell 13.86% while eCPM, revenue per thousand requests, rose 16.57%; that exchange's revenue grew 0.41%, and total revenue 1.27% once unsold requests were sold through Google's exchange.

For advertisers, floors decide which impressions are reachable at a given price and feed the bid shading models DSPs use to avoid overpaying under first price. Ad Manager's bid-level data transfer files carry a seller reserve price field beside rejection reasons.

In closed platforms such as search and retail media, the auctioneer sets the reserve, and regulators have followed. The Federal Trade Commission (FTC) opened an inquiry in September 2025 into whether Amazon disclosed reserve pricing on search ads, examining Google's internal pricing processes in parallel.

Limitations and disputes

A floor set too high turns bids into unsold inventory, and short tests may flatter the gains: the Yahoo researchers conceded their A/B framework could not capture how DSPs respond to higher costs over time. They also reported that large DSPs contractually barred intraday bid data from floor calculations and required identical floors for bidders of the same type.

Disclosure is the sharper dispute. The MRC's Digital Advertising Auction Transparency Standards, finalised on January 29, 2026, require closed-loop auctioneers to report reserve prices before and after each auction and state that floors should not be set per buyer. For OpenRTB auctions the standard only recommends managing reserves through deal IDs. That sits uneasily beside open-web antitrust cases: Teads' August 2026 complaint lists floors that could not be varied by buyeramong the conditions tying publishers to Google.

Fees blur the number further. Index Exchange introduced per-impression take rate adjustments on October 23, 2025, cutting its own fee when a bid would otherwise fall just short of a floor, and reported 4% more revenue and 45% more impressions for the Guardian in a pilot it ran. One practitioner, responding to PubMatic's fee on excess bid requests, blamed artificially high publisher floors for lost fill.

Not the same as

Soft floor. A soft floor, or soft reserve, changes what a winner pays rather than whether a bid qualifies, and has no OpenRTB field. The FTC alleges Amazon applied an undisclosed one after its auction had run; Amazon disputes the characterisation.

Deal price. In a fixed-price deal, bidfloor carries the agreed price itself, flagged by auction type 3.

Target CPM. In Ad Manager this is a floor setting that moves per request. In Google Ads the same label names an advertiser bid strategy holding average cost per thousand impressions at or below a target.

Economic price floor. Outside advertising, the term means a legally imposed minimum, such as a minimum wage.

Recent developments

Google removed unified pricing rules in December 2025, before any remedy was ordered. According to Press Gazette, the feature became plain pricing rules, with Google's example requiring $5 from one bidder and $2 from the rest. It followed an offer to the European Commission on November 13, 2025 that included buyer-specific floors; reporting dimensions under the old name were deprecated in January 2026.

Judge Leonie Brinkema then ordered on September 2, 2026 that unified pricing rules be deprecated and per-bidder floors made available, alongside real-time bid data from AdX, Google's exchange, for rival ad servers. The memorandum opinion was sealed pending redactions, and a jointly proposed final judgment is due on October 2, 2026.

Closed-loop reserves reached court that week too. The FTC and 22 states sued Amazon on August 31, 2026 over about $20 billion in alleged surcharges; according to the complaint, Amazon first referred to reserve pricing on a Support Center page on October 30, 2025. Floor setting keeps moving towards models: Magnite added dynamic pricing in place of static floors to its mediation tools in late April 2026, while IAB Tech Lab published final Programmatic Auction Definitions on June 26, 2026.

Timeline

  • 1981: Roger Myerson, and John Riley with William Samuelson, show that an optimal auction can be run as a standard auction with a reserve price
  • 1996: Jeremy Bulow and Paul Klemperer find that one extra bidder is worth more than an optimal reserve in symmetric single-item auctions
  • 1998: A sponsored search reserve of 1 cent per click is set, rising to 5 cents in 2001 and 10 cents in 2003
  • May to August 2008: Yahoo tests keyword-specific reserve prices on 461,187 keywords
  • November 2010: OpenRTB launches as a pilot between three demand-side and three sell-side platforms
  • June 30, 2011: OpenRTB 2.0 is released for comment with bidfloor and bidfloorcur in the impression object
  • April 2014: OpenRTB 2.2 adds a floor to the direct deal object
  • March 6, 2019: Google announces a unified first price auction for Ad Manager
  • May 10, 2019: Google introduces unified pricing rules, applied equally to all buyers, with an initial limit of 100 rules
  • September 5, 2019: Google begins full first price rollout after raising the pricing rule limit
  • October 8, 2019: The Prebid.js Price Floors Module is proposed on GitHub
  • June 2021: Yahoo deploys algorithmic floors on North American display inventory
  • 2022: OpenRTB 2.6 introduces mincpmpersec for video and audio
  • July 2023: OpenRTB 2.6-202307 adds durfloors for duration-based floors
  • September 2025: The MRC issues draft auction transparency standards and the FTC opens inquiries into reserve pricing disclosure at Amazon and Google
  • October 23, 2025: Index Exchange announces per-impression take rate adjustments for bids near floors
  • October 30, 2025: Amazon first refers to reserve pricing on a Support Center page, according to the FTC
  • November 13, 2025: Google offers the European Commission product changes including buyer-specific floors
  • December 2025: Google removes unified pricing rules from Ad Manager and restores per-bidder floors
  • January 29, 2026: The MRC finalises its Digital Advertising Auction Transparency Standards
  • June 26, 2026: IAB Tech Lab publishes final Programmatic Auction Definitions
  • August 31, 2026: The FTC and 22 states sue Amazon over alleged undisclosed reserve pricing
  • September 2, 2026: Judge Brinkema orders unified pricing rules deprecated and per-bidder floors available in Ad Manager

Summary

Who. Publishers, their ad servers and supply-side platforms set floors, often through vendors such as Magnite, PubMatic or specialist floor providers. Demand-side platforms read them and adjust bids. IAB Tech Lab defines how floors travel, while the Media Rating Council, the FTC, the European Commission and United States courts now police how they are set and disclosed.

What. A price floor is the minimum price, usually a CPM, below which a seller rejects bids for an impression. It is carried in OpenRTB fields including bidfloor, bidfloorcur, mincpmpersec and durfloors, and may be fixed, applied per bidder or set dynamically by a model.

When. Reserve price theory dates to 1981. Sponsored search reserves appeared in 1998, OpenRTB standardised display floors from 2011, Google imposed uniform floors across buyers in 2019 and withdrew them in December 2025, and a court order of September 2, 2026 made per-bidder floors a remedy.

Where. Floors are configured in ad servers such as Google Ad Manager, in header bidding wrappers such as Prebid.js, inside exchanges and app mediation platforms, and by the auctioneers of closed platforms in search and retail media.

Why. Floors protect inventory value when competition is thin and stop automated demand undercutting direct sales. They also reduce fill, shift bidding behaviour and can raise prices invisibly, which is why their disclosure and whether they may differ by buyer have become regulatory questions.