What Is DSP Advertising? How Demand-Side Platforms Work

DSP Advertising in One Minute

A demand-side platform (DSP) is the buyer's side of programmatic advertising. Instead of phoning a website and booking a banner, an advertiser sets a budget, picks an audience and a creative, and the DSP bids for each ad slot automatically, in the fraction of a second before a page loads.

Three ideas explain almost everything else about it:

• Programmatic: software, not a salesperson, buys the space.
• Audience first: you buy the person (for example, someone who viewed your product last week), not just the page.
• Impression-based pricing: you usually pay a CPM, the cost per 1,000 times the ad is shown, whether or not anyone clicks.

That last point is the biggest difference from search ads, where you pay per click and the shopper has already told you what they want.

How a DSP Buys an Ad, Step by Step

When a person opens a page or app that sells ad space, the publisher passes the opportunity to an ad exchange or supply-side platform (SSP). The exchange tells the DSPs who the person is likely to be and what the slot looks like. Each DSP decides whether that impression is worth buying for its advertisers, and at what price. The highest relevant bid wins and the ad loads.

• The publisher has the space (a website, app, streaming service).
• The SSP or exchange offers that space for auction.
• The DSP bids for the advertiser, using audience and budget rules.
• The advertiser sets the goal and reads the results.

The advertiser never sees most of this. What you control is the audience, the budget, the creative, the frequency (how often one person sees the ad) and the goal you optimise toward.

What It Costs: Reading a CPM

A CPM is the price of 1,000 impressions. At a $4.00 CPM, 1 million impressions cost $4,000, and 100,000 cost $400. Whether that is cheap or dear depends entirely on what those impressions do.

To see the real cost of a result, work backwards. If an ad is clicked 1 time in every 1,000 views, a $4.00 CPM means each click costs $4.00. If it is clicked 5 times in 1,000, each click costs $0.80. That is why a CPM on its own tells you little: the audience and creative decide the cost per click, and the product page decides how many clicks become orders.

Many DSPs, including Amazon DSP, are run by an agency or managed service that charges a fee on top of media cost. Ask how the fee is calculated before you sign, and get it in writing, with any change given in advance notice.

Amazon DSP: The Version That Uses Shopper Data

Most DSPs know people by browsing behaviour on the open web. Amazon DSP adds Amazon's own signals, such as people who viewed products like yours or bought from your brand before, and can show ads on Amazon, on Amazon-owned surfaces and on third-party sites and apps. It works for brands that sell on Amazon and, in many cases, for brands that do not.

reMKTR runs Amazon DSP as a managed service on its own advertiser accounts, rather than reselling access. Here is what that looked like in practice: across 30 advertisers in July 2026, the portfolio ran 78.4 million impressions at a $4.00 CPM and a blended $1.42 cost per click, with 57,137 attributed purchases at a blended $5.49 cost per acquisition. Return on ad spend was 6.04x across the whole book, and 20.1% of purchases came from shoppers new to the brand.

That is one portfolio in one month, not a promise about your account. Its use is as a yardstick: when someone quotes a DSP cost per click, ask which placements it covers. A figure for online video alone will look very different from a blend of everything.

DSP vs Sponsored Ads vs Social Ads

People often mix these up because all three are "ads you pay for". They do different jobs.

• Search or sponsored ads catch people who are already looking. Billed per click. Best for demand that exists.
• DSP ads reach people before or after they search, across many sites. Billed per 1,000 impressions. Best for reach, retargeting and building demand.
• Social ads run inside one social network's own tools, using that network's audience.

They work best together. A shopper may first see a DSP video, later search the brand name, and click a sponsored ad. Last-click reporting gives all the credit to the final click, which is why DSP often looks weaker in a dashboard than it is. Judging it fairly takes a holdout test (same audience, with and without the ad) or a combined view of both channels.

A Checklist Before You Start

• Name one goal: new customers, repeat purchases or awareness. Each needs a different audience.
• Set a frequency cap so one person is not shown the ad dozens of times.
• Decide how you will measure before launch: who designs the test, and is it written into the agreement?
• Look at new-to-brand share, not only return, so you know whether you are finding customers or re-reaching your own.
• Ask about fees: how they are charged, and what notice you get of any change.
• Check data access: you should be able to see and take your results with you.

The same questions apply to any vendor, including us.