IAB Europe on September 17, 2026 opened the first draft of a travel measurement addendum for public comment, proposing that travel media networks such as those run by Booking.com, Expedia, Kayak and Skyscanner report bookings at the moment they are made, before any trip is called off, and that a traveller be treated as new to an advertiser only after three years without a purchase. Feedback closes on October 23.

In Short

IAB Europe, a European advertising trade body, has written draft rules for how travel websites that sell ads, such as Booking.com and Expedia, report whether those ads worked. That matters to hotels, airlines and other travel companies that buy these ads, because there has been no common standard for measuring those results, so figures from different sites are hard to compare. If the rules are adopted, a sponsored hotel listing would get credit for bookings made within 7 days of the ad, a booking would be counted when it is made even if the trip is later scrapped, and a traveller would only count as a new customer after 3 years away.

An addendum, not a new rulebook

The document, titled IAB Europe Travel Media Measurement Standards and labelled "First Draft For Industry Review - September 2026", runs to nine pages. It is written as a supplement to IAB Europe's Commerce (incl. Retail) Media Measurement Standards rather than as a standalone framework. According to IAB Europe, "the majority of the Commerce Media Measurement Standards can be adopted by Travel Media Networks without change." The departures, in the draft's own words, sit "principally around look-back windows, the treatment of bookings versus sales, and the disclosure of sales extrapolation methods."

A cross-reference table at the front of the draft lists 17 metrics and standards from the parent document. Nine carry over unchanged. Five are adapted for travel: sale definitions, lookback windows, same-product and halo attribution, sales extrapolation, and the new-to-brand metric. Three are declared not relevant: the marketplace sale types used by retail networks, the new-to-category metric and the entire section on quick commerce. On new-to-category, the table notes simply that "Travel networks don't report on this metric yet."

The draft adopts its own abbreviation. "TMN" refers to the travel media network providing information directly, "or an Ad Tech provider acting on its behalf", mirroring the way the parent standards use "CMN" for commerce media networks.

The travel work was signposted. When IAB Europe opened its Commerce Media Measurement Standards V2 for comment on October 9, 2025, it said future editions would cover travel and finance. IAB Europe's own page now describes that consultation as running from September to November 2025, although it opened on October 9. The V2.1 standards, published on January 22, 2026, repeat the plan, stating that future editions would encompass "measurement standards for travel and finance media networks in 2026." Travel has now arrived in draft. Finance has not.

Attribution: 7 days for listings, 30 for display

The parent standards recommend a 30-day post-view and post-click lookback window as the default for endemic on-site and offsite media, with flexible windows available within those 30 days. The only exception so far has been quick commerce, where IAB Europe cut the default to 7 days "due to the immediate nature of Quick Commerce transactions."

Travel splits the difference by format. According to the draft, "Sponsored Products: a 7-day look-back window is the recommended standard." For display and offsite advertising, a 30-day window remains the recommended default, "with partner-level flexibility permitted." Networks are asked to offer flexible windows in addition to reporting against the default.

No rationale is given for the 7-day figure, although the same document justifies a far longer new-customer window on the grounds that travel purchases are infrequent. Why a sponsored hotel or flight listing warrants the same window as a grocery delivery is left unexplained.

Meta is named as an exception. Some off-site display, according to the draft, will need to run where "a partner enforces a shorter attribution window by default (for example, Meta)." That is a practical constraint rather than a hypothetical one. After Meta narrowed the attribution windows available in its Ads Insights API from January 12, 2026, the surviving options were 1-day click, 7-day click, 28-day click, 1-day engaged view and 1-day view. A 30-day post-view default cannot be reproduced through that interface.

Last touch by default

The draft goes further than the parent document on attribution models. It states that "the recommended industry standard attribution model for Travel Media is last-touch attribution," with multi-touch models permitted alongside it where a network can support them. The commerce standards stop short of a recommendation, observing only that return on ad spend "is typically based on a last click or view model."

Last touch has documented weaknesses in settings where shoppers compare the same room or fare across several sites. Research published in Marketing Science, covered by PPC Land in March 2025, found that last-touch attribution can underperform alternative methods when consumers see advertising across multiple publishers before converting. The draft contains no mechanism for deduplicating credit between travel networks, each of which would report its own last touch. The parent standards acknowledge the problem directly: "the lack of interoperability between Commerce Media Networks currently makes it difficult for media buyers to deduplicate investments."

Three years before a traveller is new again

Retail networks report new-to-brand shoppers against one of five purchase-cycle buckets defined in the commerce standards: 0 to 2 weeks, 3 to 6 weeks, 7 to 26 weeks, 27 to 52 weeks, and 52 weeks or more. The travel draft renames the metric new-to-advertiser and fixes a single window. "The recommended look-back window for New-to-Advertiser reporting is 3 years," according to the draft, because "travel purchases are typically infrequent relative to retail purchases."

Three years is 156 weeks, three times the 52-week mark at which the longest bucket in the parent standards begins. A hotel group advertising on a booking platform would, under this proposal, be able to claim a guest as new only if that guest had not bought from it in the preceding three years.

The working group considered a finer approach. According to the draft, it "discussed differentiating this window by destination - for example, using 500-mile increments to categorise trips," reasoning that short-haul and long-haul travel follow different purchase cycles. That idea "requires further development and is not yet part of the recommended standard." The unit, miles rather than kilometres, is unusual for a European standard; each increment would be roughly 805 kilometres.

Bookings, cancellations and price

The change most visible in a travel network's sales report concerns what a sale is. According to the draft, "Sales reporting for Travel Media is standardised on Gross Bookings (i.e. recognised at the point of booking, prior to cancellation) rather than Net Bookings." The reason given is that "the treatment of cancellations in travel differs materially from returns in retail."

In practice, a reservation called off a week after it was made would remain in the attributed figures. The commerce standards define net sale as "gross sale minus returned, cancelled, or refunded orders" and cite "anecdotal evidence" of "an average 20% delta between Gross Sale and Net Sale" in retail. The travel draft offers no equivalent figure for the gap between gross and net bookings, which leaves buyers without a published reference point for how far reported booking value may exceed stays and flights actually taken.

A contradiction in the text

The draft contains an internal inconsistency on this point. It states that gross bookings reporting "differs from the Commerce Media Measurement Standards' default assumption of gross sale." Yet gross sale is exactly the commerce default: according to the parent standards, "When the CMN doesn't specify which sale they are reporting on, it is assumed to be a gross sale." The practical difference appears to be that commerce networks may elect to report net sales if they say so, while the travel text standardises on gross. The draft does not say whether a travel network may still report net bookings alongside gross, a point the comment period may need to settle.

Base price, total price

Gross bookings can be reported on either a base price or a total price basis, and networks are asked to disclose which. Total price "can include both fees retained by the service provider and fees passed through to external parties," and a network reporting on total price "can include one type of fee or both." According to the draft, "Once again disclosure on fee types is required."

The draft sets out nine fee categories. Six are retained by the service provider: service and booking fees; baggage and seating; onboard and in-flight ancillaries such as meals, drinks and Wi-Fi; ground and property ancillaries including room upgrades, parking, breakfast and resort fees; transport and transfer add-ons such as airport transfers and car hire; and miscellaneous optional extras. Three are passed through: taxes and government charges, including VAT and air passenger duty; mandatory carrier or industry surcharges such as fuel surcharges; and insurance and protection.

The flexibility has a consequence for comparability. Two networks that both report on "total price" could be reporting different numbers for the same booking, one including taxes and one excluding them, with the disclosure note as the only guide to the difference. Regulators know the terrain: in the United States, where a federal rule requires short-term lodging sellers to show total prices, the Federal Trade Commission fined Hopper 35 million dollars over hidden booking fees in a settlement filed on July 2, 2026. The IAB Europe draft governs value reported to advertisers, not prices shown to consumers, but the fee vocabulary overlaps.

A booking replaces the SKU

In retail media, a SKU is the unit of attribution. The commerce standards require parent-SKU attribution for sponsored products, so a click on a shirt credits every size and colour variation. The travel cross-reference table states that the "equivalent of a SKU is a booking."

The explanatory sentence in the draft is garbled. It reads: "if a room at hotel was looked, all other rooms at that halo can be attributed as same booking." The apparent intent is that a click on one room type credits bookings of other rooms at the same hotel. The halo definition that follows is clearer: "Same Brand, Same Category, so another hotel owned by the same brand can get Halo attribution." Every example in this section concerns hotels. The draft does not describe how same-booking or halo rules apply to flights, car hire or packages.

Halo, as defined, stays inside one network's walls. Research from Incremental published in June 2026 estimated that siloed attribution misses 36% to 53% of retail media's total impact because shoppers exposed on one retailer buy at another. Those figures are vendor-supplied and drawn from retail, not travel, but the structural point carries over to a sector where comparison across sites is routine.

Incrementality and extrapolation

On incrementality, the working group changed nothing. The draft confirms that the definition and methodology in the commerce standards and in the Guidelines for Incremental Measurement in Commerce Media, published on November 3, 2025, "apply to Travel Media without change." The commerce standards define incrementality as the "causal impact of marketing by identifying the additional business outcomes directly driven by a campaign or tactic, compared to what would have occurred in the absence of marketing activity." They also state that a network "doesn't have to provide incrementality measurement to be certified, but if they do, they have to use one of the methods specified in the Guidelines."

Sales extrapolation is treated differently. The commerce standards describe it as a set of rules for estimating the effect of media on shoppers a network cannot identify, based on the measured effect among those it can, and ask networks to disclose which metrics the extrapolation runs through. Their example is a network assuming that sales per impression are the same for unidentified users as for identified ones. The travel draft sets its own requirement: "Organisations must disclose their use of sales extrapolation methods; the specific mathematical details of the methodology do not need to be disclosed." It does not restate the commerce requirement to name the metrics used. The draft adds that "at the time of writing, sales extrapolation is used sparingly by Travel Media Networks," and that the working group will revisit the section as usage develops.

What carries over unchanged

Media metrics transfer intact. Impressions and clicks follow IAB and Media Rating Council definitions. Viewability thresholds remain at least 50% of pixels in view for one continuous second for display and two seconds for video. Video completion rate carries over, as does filtration of general and sophisticated invalid traffic; under the parent rules, outcome measures without SIVT filtration may still be reported if they are labelled, separated and carry disclaimers.

Return on ad spend keeps its commerce definition, including the requirement to separate click-based from view-based results. So does the obligation to disclose how data reaches advertisers: through network reporting, through APIs for the advertiser's own analysis, or through data clean rooms. The parent standards list the trade-offs of each. Clean rooms, for example, offer "the largest amount of flexibility" but are "expensive" and carry "data leakage risk."

Who wrote it, and a gap in the roster

According to the draft, the working group comprised five travel media networks - Booking.com, Kayak, Expedia, Skyscanner and Marriott Media - plus two ad tech platforms that serve travel businesses, Koddi and Sojern. IAB Europe's September 17 press release names six participants: Skyscanner, KAYAK, Expedia, Koddi, Booking.com and Sojern. Marriott Media does not appear in the release. Neither document explains the difference.

The membership reflects where travel's advertising businesses sit. Koddi was founded in 2013 in Fort Worth, Texas, to serve travel advertisers, starting with hotels, and its Dusseldorf office, now its EMEA headquarters, worked exclusively on travel until its Wolt Ads partnership in May 2026; Booking.com is among its clients. On June 17, 2026, Koddi connected its commerce media network to Google's Search Ads 360, with Booking.com among the named partners. Sojern, which acquired Adphorus in 2017, had reported by the time of that deal that it had driven 10 billion dollars in global bookings and served more than 4,000 clients in 50 countries. Marriott set out plans for its Marriott Media Network in May 2022, spanning display, mobile, video, email and digital out-of-home.

Travel data has also been moving off these sites. Expedia Group routed 200 petabytes of traveller intent data through Magnite in a partnership disclosed on April 16, 2026. United Airlines put its Kinective Media network live on June 7, 2024, with Magnite's SpringServe serving inflight ads, and by March 2026 Kinective Media audiences were available in Google's Commerce Media Suite. No airline sits in the working group, and the draft is framed around sponsored listings and display.

Measurement is the recognised weak point. A Forrester study commissioned by Koddi, published in November 2025 and based on 788 senior decision-makers, found travel companies active across discovery, booking and loyalty but struggling to unify their data and prove return on investment. The research was paid for by a vendor that now sits in the working group.

What IAB Europe and the committee chair said

Marie-Clare Puffett, IAB Europe's Senior Director Industry Development & Marketing, framed the drafts as an extension of existing practice. "Measurement has always been fundamental to trust in digital advertising, and that's just as important as Commerce Media expands into new areas such as in-store Retail Media and Travel Media," she said, according to IAB Europe. "These proposals reflect months of close collaboration with retailers and travel media businesses and are designed to bring the same rigour and consistency to these fast-growing areas that the industry expects elsewhere."

Jason Wescott, Global Head of Commerce Solutions at WPP Media and chair of IAB Europe's Retail & Commerce Media Committee, said: "As Commerce Media expands into new environments and sectors, consistent and credible measurement is essential. These proposals are an important step towards greater clarity and transparency across both in-store Retail Media and Travel Media, and I'd encourage the industry to review them and help inform the final standards."

In-store proposals published alongside

A second document, proposed next steps for in-store retail media measurement, opened for comment on the same day after an IAB Europe workshop on July 1, 2026. It was not among the materials reviewed for this article, so its contents are described here according to IAB Europe's press release.

The proposal centres on a five-zone framework running from outside the store to the aisle, and a simplified opportunity to see model built on six inputs: footfall, store count, campaign duration, number of placements, aisle penetration and share of voice. Where sensors are absent, the approach favours "footfall and the opportunity for visual contact with an ad, rather than ad play alone" as the basis for an impression. Aisle penetration would be tiered, "ranging from full beacon deployment to category-level market research." Sales lift and brand sales lift metrics would be removed, and the sales reporting window aligned to 28 days.

The first in-store standards, opened for comment by IAB and IAB Europe on September 18, 2024, established store zones and format definitions. The new proposal would leave IAB Europe's commerce family with at least three default reporting windows: 30 days for standard commerce media, 7 days for quick commerce and travel sponsored listings, and 28 days for in-store sales.

The certification question

The parent standards are explicit about enforcement. "The only way to guarantee adherence to these standards is through IAB Europe's Retail Media Certification," according to the V2.1 document. A transition period allowing certification under either V1 or V2 ran until the end of July 2026; after that, only V2 applies. Albert Heijn became the first network certified in September 2025, after an audit by ABC requiring compliance with at least 90% of the programme's requirements.

The travel draft says nothing about certification. Whether a travel network could be audited against the addendum, under a programme still branded for retail media, is not addressed in either document. Nor is there a version reference that fully lines up: the draft's subtitle cites "V2" of the commerce standards, its opening section cites "V2.1", and the V2.1 PDF itself describes its contents as "V2".

The loose ends sit in a growing market. IAB Europe's AdEx Benchmark, published on July 7, 2026, put European digital advertising at 131.1 billion euros for 2025, with retail media up 16.7%. Travel's share of commerce media spending is not quantified in any of the documents.

Comments on both drafts are due by October 23, 2026, via retailmediastandards@iabeurope.eu. According to IAB Europe, "Industry feedback will help inform the further development of the addendum ahead of final publication." No date for the final version has been given.

Timeline

Summary

Who: IAB Europe, through a working group of travel media networks (Booking.com, Kayak, Expedia, Skyscanner and, according to the draft though not the press release, Marriott Media) and the ad tech platforms Koddi and Sojern. Marie-Clare Puffett of IAB Europe and Jason Wescott of WPP Media, chair of IAB Europe's Retail & Commerce Media Committee, commented on the proposals.

What: A nine-page first draft of Travel Media Measurement Standards, written as an addendum to IAB Europe's Commerce (incl. Retail) Media Measurement Standards V2.1. It proposes a 7-day lookback window for sponsored products and 30 days for display and offsite, last-touch as the recommended attribution model, a 3-year new-to-advertiser window, gross bookings recognised before cancellation, base or total price reporting with fee disclosure, a booking as the equivalent of a SKU, unchanged incrementality rules and mandatory disclosure of sales extrapolation. In-store retail media measurement proposals were published at the same time.

When: Both drafts opened for public comment on September 17, 2026. Feedback is due by October 23, 2026. No date for final publication has been set.

Where: IAB Europe is based in Brussels and the standards are intended for European markets. Comments go to retailmediastandards@iabeurope.eu.

Why: Travel networks sell advertising against booking data without a common European measurement standard for reporting results. IAB Europe had committed in 2025 and again in January 2026 to extend its commerce standards to travel. The draft leaves several matters open, including the rationale for the 7-day sponsored window, the comparability of "total price" reporting, garbled same-booking wording, an internal contradiction on gross sales, an unexplained discrepancy in the working group roster and the absence of any reference to certification.