What Is Post-Bid and What Are Its Pros and Cons?

Reading time: 5 minutes

Programmatic ad bidding has come a long way. Once upon a time, we used the waterfall technique (also referred to as daisy chaining), which came with a lot of inefficiencies. From there, we’ve moved on to header bidding[5] (also referred to as pre-bid or pre-bidding) which is a more advanced technique designed to solve the inefficiencies programmatic ad buyers and sellers were experiencing with daisy chaining.

Header bidding allows publishers to essentially call upon all the demand sources simultaneously participating in an ad auction. It also allows publishers to control which of these sources specifically participate in the process with the idea that it’ll help publishers to increase their overall yield[11] and revenue with each auction.

While this comes with several advantages, such as increased transparency[6], eCPM[1], revenue, and control, there is one huge drawback: Page latency.

However, depending on your header bidding provider or infrastructure, you can reduce this latency to a certain extent. While publishers can implement header bidding on their own, there are quite a few prerequisites they must meet to partner with SSPs. Setting up an ad server also takes a bit of technical knowledge. 

So, what happens if you’re a publisher[12] who doesn’t have the right resources or technical know-how to properly leverage header bidding?

The answer is: Turn to post-bidding (or, post-bid).

What is Post-bidding, you ask? Keep reading to find out.

So, What Exactly Is Post-Bid or Post-Bidding?

Post-bidding, aka post-bid, is a different way for publishers to connect directly with multiple demand sources and run simultaneous auctions to garner the best bids for their ad inventories. 

If it sounds a lot like header bidding, it’s because it is — but with one very significant difference. With post-bid, the unified auction doesn’t happen until after the ad creative from the post-bid line item[13] has been delivered (hence the name). 

You’re probably wondering, how can an auction even happen if the ad creative[14] has already been delivered? 

Put simply, in the post-bid world, an as creative is nothing more than a prebid.js tag — which is a third-party tag. Therefore, if the post-bid line item ends up winning the auction, then the ad creative or, prebid.js, will be rendered on the page. In turn, this action is what calls the demand partners, runs the auction, and serves the ad from the highest bidder[15]

How Does Post-Bid Work?

Post-bidding can come off as a bit complicated, so here’s the complete process simplified:

  • From there, the ad server will pick up the right line items in order[16] to sell the impressions in a unified first-price auction. (Just for the record, a unified-first price auction is another programmatic technique that allows multiple demand sources to compete simultaneously for the same ad slot versus in sequence)
  • If the ad server calls on the post-bid line item and that post-bid line item wins based on its historic price, then the ad creative will go on to render on the page in the specific ad slot 
  • In the case of the ad creative being Prebid.js, it’ll initiate the bidding process as normal. This means it’ll call upon all the demand partners to run the simultaneous auction
  • The winner’s ad will then get rendered to the user on the page

What Are the Benefits of Post-Bid?

There are several advantages that come with implementing post-bid, including:

The Setup Doesn’t Call For Engineering Assistance or Other Resources

As mentioned earlier, post-bidding doesn’t depend on an in-house technical team or a specific infrastructure. That means it doesn’t count on special coding or the use of wrapper tags

The only “technical” work involved is placing tag ID (prebid.js) into the third-party tag’s JSON configuration — similar to your regular line item setup.

There’s Reduced Ad Latency

With post-bidding, the ad server rejects the initial impression[8] and jumps straight to the post-bid. Therefore, any additional ad serving time gets shaved off to focus on the auction. In other words, the auctions start as soon as the ad creative is served which means there’s no ad latency as there would be with header bidding or the traditional waterfall auction.

You Can Set Up a Fallback

In some cases with post-bid auctions, there won’t be a winning demand partner for the impression. When this happens, the publisher usually ends up serving a blank impression[4].

Post-bid line items can be optimized with their own fallback setting (or in-house line items) to prevent this type of thing from happening. By having a fallback setting, a winning bid[9] is guaranteed.

Are There Any Drawbacks?

Post-bidding does come with a few drawbacks as well. These drawbacks include:

Revenue Uplift Likely Won’t Be as Great as Header Bidding

With header bidding, your revenue is typically predicted to jump by up to 50%, at least. This is because with header bidding you get a real-time price for your ad impressions from all the demand partners involved. From there, their bids are sent to the ad server for another round of auctioning with the same demand sources and direct line items.

However, in a post-bid, GAM automatically picks the post-bid line item based solely on the history price — not real-time price— since the creative is already delivered. This takes away most of the competition, leaving publishers with less.

There’s No Dynamic Allocation

If an impression gets rejected by an ad server, the responsibility of getting an ad creative falls on the post-bid. This makes the post-bid line items a one-shot deal, in a sense whereas, with header bidding, publishers are able to run multiple auctions at once to dynamically choose a winner in real-time.

There’s Potential For Browser Overload

If there are multiple ad units on a page, it can result in multiple simultaneous auctions. 

For example, say there are two ad units on a page and both of them are ready to serve the post-bid ad. When this happens, two separate auctions end up happening (at the same time) which can overload the browser.

Reporting Can Be Pretty Difficult

With post-bidding, you can really only get aggregated reporting — not granular reporting. This is because, with programmatic reporting, ad servers aren’t capable of generating efficient reports in regards to post-bidding because it would require separate bids for all the demand sources participating in the auction.

Therefore, publishers must rely on third-party reporting or more detailed wrapper[10] tags to get the details they want from their demand partners. 

Should You Try Post-Bidding?

Post-bidding can help you run auctions on the client-side, which can bring you better match rates. It also allows you to form direct relationships with your demand partners and brings more transparency to the table while reducing latency — all in comparison to header bidding, of course.

Having said that, if latency is your only issue, then turning to the post-bid way of auctioning shouldn’t be your first alternative solution. This is because there are plenty of ways to resolve latency issues, such as bidder-level optimization, universal timeout, etc. Additionally, GAM also runs unified first-price auctions, so you don’t have to run a post-bid for simultaneous auctions.

However, if you don’t have the resources to run your header bidding auctions more efficiently by using managed solutions or otherwise, then post-bidding would be your alternative solution.

1. Effective Cost Per Thousand Impression [eCPM] ( eCPM ) eCPM is known as the effective cost per thousand impressions and is a metric used by publishers to determine the actual rate they’re earning from their ad inventory. eCPM is calculated by taking your (total ad earnings/impressions) x 1000.
2. Google Ad Exchange ( Google Ad Manager ) Ad Exchange is often referred to as the premium version of AdSense, and also a Google-owned ad network of sorts. To join Ad Exchange, publishers need to meet specific requirements such as 500 000 minimum monthly traffic, be invited or join through a Google certified partner. Recently Google has rebranded this product, and it is now called Google Ad Manager.
3. Google Ad Manager ( GAM ) Google Ad Manager is a combination of both Google Ad Exchange and DoubleClick For Publishers as a unified platform that provides publishers with ad serving services.
4. blank impression. Blank impressions are also known as blank ads or unfilled impressions and occur when blank ads are displayed on a website. No publishers want blank impressions as these ads don’t result in ad revenue. Many reasons for blank ads can exist such as not having enough advertiser demand, low page loading and having too high CPM floors.
5. header bidding. Header bidding is an ad technology that allows publishers to earn to most ad revenue possible for their ad inventory by ensuring the highest bidding ad is served.

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