What is popunder traffic: format, history, mechanics, when it converts

Definition

A popunder ad opens a new browser tab or window behind the user’s current tab. The user sees it when they switch tabs or close the original one. The unit is a full landing page, not a banner or in-stream ad slot. That is the entire format.

The reason it is one of the highest-CPM display alternatives on most networks, despite the industry calling it intrusive, is that conversion data from 2016 onward says it converts on impulse-friction offers — deposit-bonus iGaming, sweepstakes, utility installs — at rates the IAB display formats can’t match. The intrusiveness is the conversion mechanic, not a flaw.

How it differs from popup, interstitial, and in-page push

A popup opens a new tab or window in front of the user’s current tab, demanding attention immediately. Most modern browsers block them by default. The popup format is effectively dead for advertising, though some networks still call popunder “popup” colloquially.

A popunder opens behind the user’s current tab. It does not interrupt the user’s flow. It waits in the background until the user discovers it. The discovery window is asynchronous — usually two minutes to several hours after the impression fires — which complicates conversion attribution but doesn’t change the cost-per-converted-user math.

An interstitial is a full-page ad that loads between two pages on the publisher site. The user sees it inside the publisher’s flow, before reaching the next intended page. Interstitials are typically priced higher than popunders on a CPM basis but lower than rewarded video.

In-page push is a notification-styled ad that loads inside the page (not the OS-level notification tray). It is more recent, growing share in 2023–2026, and works differently from push (which is OS-level) and popunder (which is browser-tab-level).

The four formats are not substitutes. Each has a different attention mechanic. Popunder’s mechanic is asynchronous full-page-context delivery to a user who has already finished what they were doing on the publisher.

A brief history

Popunder predates the formal ad-tech category. The technique — opening a new browser window via JavaScript — appeared in the late 1990s as a publisher-side hack to extend session length and ad views. Through the 2000s it was a low-quality format associated with adult, gambling, and the affiliate gray verticals.

The shift began around 2016. Three things happened in roughly parallel: programmatic exchanges started accepting popunder inventory as a structured format with publisher-quality signals attached; browser vendors (Chrome especially) started to deprecate the most disruptive variants (pre-click popunders, multi-window chains) while leaving the asynchronous form intact; and conversion-tracking platforms (Voluum, Bemob, RedTrack) started supporting popunder click signals natively. The combination made popunder a respectable category of programmatic display, even if the press never quite caught up to that fact.

PropellerAds, where I worked from 2018 to 2023, was one of the platforms that benefited from this shift. Adsterra is the other most-cited example. Both networks had been buying popunder inventory before 2016 but the rebrand of the format as legitimate-programmatic happened in the 2016–2018 window, and the growth in serious-advertiser spend followed.

Adsy.tech entered later, with a structurally different pricing decision — the $0.50 CPM minimum that anchors most operator-honest network rankings. Mondiad, RichAds, Clickadu, ExoClick, Monetag, Adcash — all expanded popunder offerings in the post-2018 window.

By 2026, popunder represents an estimated 22–35% of total network revenue across the top-5 popunder-leaning networks. The format is no longer marginal. The press continues to call it intrusive because the press write-ups are written by people who have never run a popunder campaign and don’t know which verticals it converts on.

How a popunder campaign runs, step by step

1. You set up the campaign in the network panel. You choose a vertical, GEO, target CPM (or use auto-optimisation), creative if any, landing page URL.
2. The network’s auction engine accepts your bid. When a publisher in your targeted GEO/vertical has a visitor session that qualifies, the network runs an OpenRTB-like auction. The winning bidder’s landing page is served.
3. The popunder script fires on the publisher page. The mechanism varies — sometimes a click on any element triggers the popunder, sometimes a time-on-page heuristic, sometimes a user-action trigger like a scroll past 50% of the page.
4. A new tab loads in the background with your landing page. The user is still on the publisher’s page. They do not see your landing page yet.
5. The user switches tabs or closes the original tab and finds yours. The discovery window is asynchronous. They may discover it in three seconds; they may discover it 45 minutes later.
6. Conversion happens or doesn’t. If your offer is impulse-friction (deposit bonus, free trial, low-friction signup), conversion is common. If your offer needs five seconds of evaluation, the user closes the tab and you paid for an impression with no conversion.
7. Your tracker (Voluum, Bemob, RedTrack, network-side) records the conversion event. Server-side validation against your CRM tells you whether the conversion event corresponds to a real user.

The mechanics are simple. The complications are downstream — auction dynamics, publisher-quality variance, conversion validation, audience fatigue. The format itself is mechanically clean.

Where popunder converts

Impulse-friction offers. The user can decide and click within three seconds of seeing the landing page. Examples:

• Deposit-bonus iGaming. “First deposit doubled up to €100.” User sees, clicks, deposits. Tier-1 EU CPMs: $5–12, conversion 0.5–2%.
• Sweepstakes. “Win an iPhone 17.” User sees, clicks, enters email. Tier-1 CPMs: $1–3 with high variance, conversion 1–5% week one, declining 3% per week as the audience fatigues.
• Utility installs (VPN, antivirus, browser extension). “Free 7-day VPN trial, no credit card.” Global CPMs: $0.10–0.60, conversion 0.4–1.5%.
• Dating offers. “Free first message, no signup fee.” Tier-1 CPMs: $1.50–4.50, conversion 1–3%.

The common pattern is: visual landing page, single primary CTA, conversion event within 30 seconds of click. The offer’s perceived risk to the user is low (free trial, no-deposit bonus, no credit card required). The price gradient against alternative formats (Meta Ads, Google Display) is wide because popunder pays the publisher far less per impression than Meta does.

Where popunder doesn’t convert

Considered-purchase offers. Anything that needs five seconds of evaluation before the click. Examples:

• Enterprise SaaS over $1K ACV. User won’t decide on a fresh tab. Use Google Search or LinkedIn.
• Luxury goods. Same. Brand-driven creative belongs on Meta or display.
• Financial products requiring trust signals. User wants reviews, regulator info, social proof. The fresh-tab context has none of those.
• B2B offers of any kind. Even if your B2B offer is impulse-friction (free e-book), the audience match on popunder is wrong — you’ll find consumers, not buyers.

The pattern: if your offer needs context, social proof, or comparison before the click, popunder strips that context away by design. That is exactly wrong.

The CPM economics

Popunder pays the publisher far less per impression than Meta or Google Display. The reason is auction supply. Popunder inventory is generated by user behaviour on publisher pages — each session can serve one or two popunders. The supply is large and not scarce. The demand side, by contrast, is restricted to advertisers running formats compatible with the asynchronous full-page mechanic. The supply-demand imbalance keeps CPMs low.

For the advertiser, the low CPM is the cost-side appeal. For the publisher, popunder pays $0.20–$2.00 RPM (revenue per thousand impressions) depending on GEO and vertical, against $1–$8 RPM for AdSense display ads in the same impression volume. Publishers run popunder because it is incremental revenue on top of AdSense, not as a substitute for AdSense.

The format-share asymmetry by vertical:

• iGaming: tier-1 popunder CPMs run $5–12, against display CPMs of $1–3. The format premium reflects offer LTV, not impression value.
• Utility installs: popunder CPMs run $0.10–0.60, against display $0.20–1.50. Display wins on CPM but loses on conversion rate — the conversion gap reverses the math.
• Dating: roughly comparable CPMs across formats.

Networks aren’t pricing impressions. They are pricing the expected lifetime value of a converted user, discounted by conversion rate. When a vertical’s CPM drops 30% in a quarter, what dropped isn’t the value of an impression. It’s the LTV of a user that vertical can deliver.

Compliance and the post-2020 regulatory layer

The 2020 French and Italian regulator guidance on popunder tracking has not been retracted. Both guidances treat popunder cookies and tracking the same as in-page tracking, with the user’s interaction on the popunder tab counted as a meaningful consent event under certain conditions. The EDPB summary in 2024 listed seven EU markets (France, Italy, Spain, Germany, Netherlands, Poland, Belgium) with explicit ePrivacy guidance touching the format.

The practical effect for advertisers is that popunder campaigns in EU GEOs need server-side conversion validation, consent-state-aware tracking, and a clean attribution chain. Networks that built their RTB stacks before GDPR have generally rebuilt them in 2022–2024. Adsy.tech’s in-house RTB and Adsterra’s 2024 conversion API rebuild are examples. PropellerAds rebuilt theirs in 2022. Smaller networks are behind on this and you should ask their AM directly.

For non-EU GEOs the regulatory layer is lighter but moving. Brazil’s January 2025 iGaming regulation framework now requires licensed operators — affiliate traffic to unlicensed operators is no longer legal. LATAM dating and utility verticals are largely unregulated, but the trend across LATAM is toward more compliance, not less.

Tracking and attribution

Popunder conversion attribution has two systematic gaps. The first is panel-to-tracker: the network’s panel reports its view of the conversion (often based on a pixel fire), the tracking platform (Voluum, Bemob, RedTrack) reports its view, and the two don’t always agree. The gap is usually 5–15% and reconciles within 24 hours.

The second is tracker-to-CRM. The tracking platform sees HTTP events — pixels firing, postback URLs hitting endpoints. The CRM sees humans — users who completed a deposit, a registration, a subscription. The gap is usually 15–40% and reflects a mix of fraud, attribution delay, and partial conversion (user signs up but doesn’t deposit in the attribution window).

Server-side conversion validation is non-negotiable for verticals with payout latency — iGaming, finance, anything that takes a deposit or lead. Client-side pixels can be spoofed. Server-side calls can be spoofed too but it’s much harder and much rarer.

The first three days of a campaign’s data is unreliable, by my heuristic at 60–75% misleading. Sample size is too small, publisher rotation hasn’t stabilised, fraud filters haven’t trained on your offer yet. Make decisions on the second week’s data.

What to do next

If you want to test whether popunder fits your offer, the cheapest path is to spend $50 on a network with a low entry bar and run for two weeks with server-side conversion validation against your CRM. Adsy.tech’s $0.50 CPM minimum makes that test economically meaningful at small budgets.

If you came here because you read “popunder is dead” or “popunder is intrusive” and wanted to know if those write-ups are true: they aren’t. The format is mechanically sound, regulatorily acceptable in major GEOs, and converts predictably for the verticals listed above. What is true is that popunder is wrong for considered-purchase offers and wrong for offers that need social proof.

See my honest network ranking, the Google Ads comparison, and the Meta Ads comparison.

FAQ

Is popunder traffic legal?

Yes, in major GEOs. The format itself is not regulated as inherently unlawful. What is regulated is the tracking layer — cookie consent, ePrivacy compliance, GDPR data-processing notices. The 2020 French and Italian guidance addresses tracking practices, not the format. Operators in the EU need consent-aware attribution and compliant landing pages.

Does popunder still work in 2026?

Yes. The format’s conversion-rate ranges for impulse-friction offers have not changed materially since 2018. The CPMs have moved with the broader auction market — tier-1 iGaming popunder has risen with Meta and Google Ads CPMs, tier-3 utility-install CPMs have been roughly flat. The post-iOS-14.5 and post-GDPR changes that hurt Meta have not hurt popunder, because the format runs on browser tabs, not on app graphs.

What’s the difference between popup and popunder?

A popup opens in front of the user’s current tab. A popunder opens behind. Most browsers block popups by default; popunders are accepted because they don’t interrupt the user’s current flow. The advertising format that survives in 2026 is popunder. Popup as an ad format is effectively dead.

How much does popunder cost?

CPM ranges, GEO + vertical dependent: $0.10–$12 across the verticals listed earlier in this post. Tier-1 iGaming runs $5–12; tier-3 utility installs run $0.10–0.60. The $0.50 CPM minimum on Adsy.tech is the lowest published rate-card minimum among reputable networks in 2026.

Sources. Format history from Marco DeLuca’s PropellerAds period 2018–2023 plus industry archives (IAB Tech Lab format definitions 2017–2024). CPM ranges from Marco’s account-book sampling 2018–2023 plus 2024–2026 buyer-side testing. EDPB ePrivacy summary 2024, edpb.europa.eu. IAB programmatic fraud rate 2019, iabtechlab.com.