What is a Post Bid? What are the Pros & Cons of Post Bidding for Publishers?

Header bidding — a technique that started to deal with the inefficiencies from the waterfall technique or daisy-chaining, eventually became the de facto way of running programmatic auctions. If you’re a digital publisher looking to move past ad networks and Google Ad Exchange, you’re likely to end up implementing header bidding (client-side or server-side). 

While there are several advantages, including — a jump in eCPM & revenue and increased transparency & control, page latency has been considered a drawback that should be addressed. 

If you use a managed header bidding provider, you’re sorted out. For example, at Mile, we continually invest and maintain our server-side infrastructure to ensure our publishers aren’t facing any latency issues. On the other hand, if you have an in-house team and extensive resources (team & infrastructure), you’ll be able to reduce the latency to an extent. At the end of the day, latency wouldn’t be an issue. 

So, if you are a publisher who doesn’t fall in either of the two buckets and still want to leverage header bidding, meet — Post bidding. 

Sidenote: You can implement header bidding (or pre-bidding) yourself. But there are prerequisites to partner with the SSPs and ad server setup requires at least some technical know-how.  

So, What is Post-Bid or Post-Bidding?

Post-bidding is a way for publishers to directly connect with multiple demand partners and run simultaneous auctions to get their best bids — after the ad server delivers the creative. 

Yes, it’s the same as header bidding or pre-bidding, but with one important difference — a unified auction happens after the ad creative from the post-bid line item is delivered. Hence the name, post-bidding. 

Let us show in a simple diagram: 

Before we get into how it works, its advantages or disadvantages, or the difference between post-bid and pre-bid, you should have this question in mind. How can an auction happen once the creative is delivered? Well, in post-bid, ad creative is nothing but a prebid.js tag (a third-party tag). So, if the post-bid line item wins the auction, then the creative or prebid.js will be rendered on the page. This, in turn, will call the demand partners, run the auction, and serve the ad from the highest bidder. 

What is Post Bidding vs. Pre-Bidding?

While most of the publishers start with pre-bidding, it is essential to know the difference between the two. Both approaches involve different strategies for auctioning ad impressions, and each has its own set of advantages and challenges. By comparing these methods, you can make informed decisions about which approach best aligns with your goals:

Timing of the Auction: In pre-bidding, the auction takes place before the ad server is called. Here, multiple demand partners submit their bids in real time, and the highest bidder wins the impression. In contrast, post-bidding involves running the auction after the ad has been served. The ad server first delivers the ad to the user, and then the auction takes place to determine the final price that advertisers will pay.

Impact on Revenue: With pre-bidding, you can typically know what your revenue is going to be before the ad is served. Simply put, the competition among demand partners before the ad server call can drive up bids, leading to potentially higher revenue within the range you calculated. However, in post-bidding, since the auction happens after the ad is served, the final price can be highly dynamic and will be a reflection of the real-time value of the impression, which can be either higher or lower.

Control over Ad Inventory: Pre-bidding allows publishers like you greater control over your ad inventory. Here, you can set price floors, set priority for select demand partners, and better manage how your inventory is allocated. On the other hand, the post-bid auction can provide more accurate pricing based on immediate demand – which means publishers have less control over their inventory.

Speed and Performance: Prebid involves making multiple ad calls before the ad server is reached. While this can increase competition and potentially drive up bids, it can also lead to slower page load times, as multiple requests are being processed before the ad is finally displayed. However, post-bid has the advantage of offering faster page load times as the ad server handles all ad calls after the ad has been served.

Snapshot: Prebid Vs. Post-bid

How Does Post-Bid Work?

Source: Prebid

To understand how post-bid works, let’s break down the process step by step:

Step 1: Page Load and Ad Server Call

When a page loads, it makes a call to Google Ad Manager (GAM) via Google Publisher Tag (GPT). This initial call sets up the framework for ad serving.

Step 2: Unified First-Price Auction

The ad server then selects the appropriate line items for selling the impressions through a unified first-price auction*. This means that all participating bids are considered, and the highest bid wins the impression.

Step 3: Post-Bid Line Item Evaluation

If the ad server identifies a post-bid line item and it wins the auction based on historical pricing data, the ad creative associated with that line item will be rendered in the designated ad slot on the page.

Step 4: Initiating Post-Bid Auction

At this stage, if Prebid.js handles the ad creative, it triggers the typical post-bid auction process. Prebid.js calls various demand partners simultaneously to run real-time auctions for the impression.

Step 5: Ad Rendering

The winning ad from the post-bid auction is then displayed to the user in the ad slot.

What are the Benefits of Post-Bid?

After understanding the difference between pre-bid and post-bid, it has become quite clear that post-bid also has a few other advantages:

1. Easy to implement: You don’t need a lot of resources and ad ops engineers or devs to implement it. As it’s similar to any regular line item setup, the only exception is that you add prebid.js in place of a third-party creative tag, and the system takes care of the rest. Once the tag is in place, Prebid.js handles the auction across all demand sources each time a post-bid line item wins. It’s comparatively easy to get started, which makes it a great option.
2. No added latency: The auction starts once the ad creative is served on the page, and this means there’ll be no latency. In fact, post-bidding often runs faster than pre-bidding by calling all demand sources simultaneously, improving overall page performance.
3. Added flexibility using Fallback Options: Post-bidding provides flexibility by allowing you to configure fallback options for unsold impressions. If the post-bid auction doesn’t fill an impression, you can set it to default to a house ad or another fallback option. This ensures that all inventory is monetized effectively, even when primary auctions or direct-sold campaigns fail to fill the impression.

But,

Are there any Drawbacks?

Yes, it has its drawbacks. We’ll start with the most important ones. 

1. Revenue from post-bid can not be predicted: Revenue uplift won’t be as great as header bidding. In header bidding, your revenue can jump substantially (by up to 50%), but in post-bid, it’s not the case. Why?

In header bidding, you get a real-time price for your ad impressions from the multiple demand partners and then send their bids to the ad server for another round of auction with the demand sources and direct line items configured inside the server. In post bidding, GAM picks the post-bid line item based on the historical price (not real-time), as the real-time auction happens only after the creative is delivered.

Another problem is, as it’s not the real-time price, you aren’t allowing demand partners to compete with AdX on an even footing. 

2. Add load due to multiple post-bid auction on single page: Multiple ad units on the page can result in multiple simultaneous auctions. Let’s say you have two ad units on the page and both of them are about to serve the post-bid ad, then there’ll be two separate auctions happening and this can overload the browser.

But it won’t affect the content on the page as content can load before the auctions. 

3. Lack of detailed reporting: You can’t get granular reporting; only aggregated. You need to use a third-party analytics provider to get the bid-level data for the individual demand partners. 

Should You Try Post-Bidding?

Post-bid programmatic can help you run the auction on the client-side (so better match rates), have direct relationships with the demand partners, and provide transparency. It can reduce the latency compared to header bidding. 

That being said, if you’re planning to try out post-bidding — just because header bidding causes latency, don’t. You can resolve latency issues to an extent with a universal timeout, bidder-level optimization, etc. And besides, the header bidding script is asynchronous (it won’t even block the other content from loading). Else, you can consider footer bidding. The practice of running header auctions once the page elements/content are loaded.  

As Google Ad Manager itself is running the unified first-price auction, you don’t have to run post-bid for the reason of parallel/simultaneous auction as well. 

But if you don’t have the necessary resources and wouldn’t want to use any managed header bidding solutions, then post bid can work for you. 

People Also Ask

Ques: What is post bid vs pre bid?

With pre-bidding, the auction happens before your ad even gets shown. Demand partners submit their bids when the user opens the page, and the partner with the highest bid wins, though it might slow down your page load speed.

On the flip side, post-bidding takes place after the ad is already on display. It can be a bit unpredictable and offers less control, but it keeps your page loading faster and can capture real-time demand.

Ques: What is the difference between "Header bidding," "Prebid," and "Post-bid"?

"Header bidding" is a method where an auction among multiple demand partners occurs before the ad server is called, typically in the web page's header.

"Prebid" is the most popular open-source solution for implementing “Header Bidding”. This solution manages the auction process before the ad is served.

"Post-bid" means the auction is conducted after the ad has already been displayed to the user. This method allows for real-time pricing of the impression based on performance or user interaction, though it can lead to more variable revenue.

In short, header bidding is the overarching concept. Prebid is a specific tool for pre-bidding, and post bidding happens after the ad is served.

Ques: How does post-bidding impact page load times?

Since the auction occurs after the ad is already served, users don’t experience delays waiting for multiple ad calls to complete before the ad appears – which happens in the case of pre-bidding.

Ques: Is post-bidding suitable for all publishers?

Post bidding can be a great option for some publishers, but it’s not a one-size-fits-all solution. If you are a publisher who prioritizes fast page load times and is open to experimenting with dynamic pricing, then you should definitely implement it. However, you should be willing to face the variability in revenue while implementing post-bidding. If you are a small publisher, you might find pre-bidding or other auction methods more suitable as it requires technical know-how.

Ques: Is post-bidding suitable for mobile apps?

Yes, post-bidding can be particularly effective in serving ads in mobile apps, as fast load times can play a critical role in maintaining user engagement. This method reduces the number of initial ad calls, leading to quicker ad serving. However, you can ensure that the auction happens smoothly after the ad is served to avoid any issues on mobile platforms.

Ques: If the post-bid demand sources are unable to fill, can I still pass back the impression to another tag, like from AdSense?Yes, if none of your post-bid demand sources fill the impression, you can implement a passback to another ad tag, such as AdSense. This ensures that your ad inventory is not left unsold, allowing you to still generate revenue. It’s a good practice to have a fallback option like AdSense in place to maximize fill rates and avoid losing out on potential earnings. However, make sure that your ad server and post-bid setup are configured to handle these passbacks smoothly to avoid any delays or issues with ad delivery.