A specific, confident claim circulates across e-commerce marketing blogs: back-in-stock alerts sent within five minutes of restock convert 45% higher than ones sent an hour later, credited by name to Omnisend. We checked Omnisend's own site directly. No such report exists there — not that number, not that study, no link to either. That's one example in a small genre of very precise, very citable-sounding back-in-stock statistics that, on inspection, don't trace to where they claim to come from.
This piece separates what actually holds up — real (if occasionally self-contradicting) vendor benchmark data, two genuine randomized controlled trials on message-channel effects, and a body of peer-reviewed consumer-psychology research on scarcity — from the invented multipliers, misattributed studies and drifting numbers that dominate this specific corner of e-commerce content. It also covers what stockouts actually cost, and what to build first once the fake stats are out of the way.
Key takeaways
- Back-in-stock email performance is genuinely strong, but even the same vendor contradicts itself: Omnisend's own site publishes three different numbers for the same automation across three separate pages (open rates of 58.80% and 59.19%; conversion rates of 5.34%, 6.46% and 6.72%). A widely-repeated "65.32% open / 24.49% click / 14% conversion, per Barilliance" combo stat is only one-third real — the open rate is genuine, the other two figures don't appear anywhere on Barilliance's actual page.
- Every specific WhatsApp-beats-email multiplier we checked failed a source check. A "98% WhatsApp open rate" claim turns out to describe SMS and WhatsApp combined on the page that states it. A "3x higher recovery" claim attributed to Hellmann's, Adidas and IKEA cites a Meta/Shopify report that doesn't exist. An "18-25% WhatsApp conversion" stat is attributed to a company that, per its own site, doesn't offer WhatsApp yet.
- The most rigorous real evidence on message channel — two peer-reviewed randomized controlled trials, run outside e-commerce — found SMS and email produced statistically indistinguishable behavioral outcomes (P = .52 and P = .84 in one; an overlapping confidence interval in the other). One real single-retailer case put email and SMS conversion within a point of each other, even while SMS drew nearly three times the click rate.
- Every specific "send within N minutes for X% more sales" timing claim we checked was fabricated or misattributed, including two separate claims credited to Klaviyo and Omnisend that don't appear on either company's own site. The one real, dated case study we found — a 2011 back-in-stock program that still ran a strong 22.45% conversion rate — sent its alerts once a night in a batch, not instantly.
- Scarcity psychology is real, peer-reviewed and dates back fifty years — but none of six studies we checked, including a 2022 meta-analysis of 416 effect sizes, supports one clean "scarcity increases sales by X%" number. The specific multipliers that circulate on scarcity-marketing listicles (up to 226% more sales, a 30% Baymard figure, a 332% conversion jump) don't trace to the institutions they're attributed to, and the numbers shift between retellings of "the same" stat.
How much do stockouts actually cost — and does the $1.75 trillion number check out?
Two very large, very different-looking numbers circulate for the same underlying problem, and they don't measure the same thing. The one still repeated most often — $1.75 trillion — comes from a 2015 IHL Group study sponsored by OrderDynamics, "Retailers and the Ghost Economy." It's a real, dated study, but it isn't a stockout number: $634.1 billion of it is out-of-stocks, $471.9 billion is overstocks, and $642.6 billion — more than a third of the total — is preventable returns. A decade of blog posts have stripped that breakdown and repeated $1.75 trillion as if it measured lost sales from empty shelves alone.
IHL Group's more recent numbers are cleaner. A 2018 analysis (reported via Supply Chain Dive), based on a study of roughly 600 households and several retailers, put worldwide out-of-stock losses specifically at $984 billion, with $144.9 billion of that in North America. Its 2023 figure, reported by The Food Institute, widens the lens back out to "inventory distortion" — $1.77 trillion combined, split into $1.2 trillion from out-of-stocks and $562 billion from overstocks.
| Source | What they report | Basis |
|---|---|---|
| IHL Group, 2023 (via The Food Institute) | $1.77 trillion lost worldwide to inventory distortion in 2023 — $1.2 trillion from out-of-stocks, $562 billion from overstocks | Global retail analysis; full underlying methodology not detailed in the public summary |
| IHL Group / OrderDynamics, "Retailers and the Ghost Economy" (2015) | $1.75 trillion — but this bundles out-of-stocks ($634.1B), overstocks ($471.9B) and preventable returns ($642.6B), not stockouts alone | 2015 study sponsored by OrderDynamics; still circulates today mislabeled as a pure stockout figure |
| IHL Group, 2018 (via Supply Chain Dive) | $984 billion lost worldwide to out-of-stocks specifically — $144.9 billion of that in North America | Study of roughly 600 households and several retailers |
| Baymard Institute | 68% of e-commerce sites don't allow an order on a temporarily out-of-stock product; 30% of shoppers abandon to look for the product elsewhere when simply told it's out of stock | Usability testing / UX benchmark research |
$1.77 trillion
lost worldwide to inventory distortion in 2023 — $1.2 trillion of it from out-of-stocks alone
Source: IHL Group, 2023 (via The Food Institute)
A commonly repeated line — "39% of shoppers go straight to a competitor when they see an out-of-stock product, per Baymard" — doesn't hold up. We checked Baymard's actual out-of-stock research directly: it contains a 30% figure (abandon to look elsewhere, not competitor-specific) and a 68% figure (sites blocking orders entirely), but no 39% statistic and no competitor-specific claim anywhere on the page.
Do back-in-stock emails actually outperform other campaigns?
By the numbers vendors publish about their own platforms, back-in-stock is a real standout — it's just that the same vendor doesn't always agree with itself. Omnisend's 2025 email marketing benchmarks (20 billion-plus campaign emails, 470 million automated sends, 27,000-plus brands) credit back-in-stock with the highest revenue per email ($9.14) and the highest conversion rate (6.72%) of any automation type it tracks — though not the highest open rate; that crown goes to shipping confirmation, at 62.67% against back-in-stock's 58.80%. Back-in-stock's other numbers on that page: a 21.31% click rate, used by only 0.6% of brands. A separate page on Omnisend's own site puts back-in-stock's open rate at 59.19% and its conversion rate at 5.34%. A third Omnisend report — its 2026 e-commerce marketing report, covering 150,000 brands and 27 billion emails sent in 2025 — states that back-in-stock delivered the highest conversion rate (6.46%) of any automation type. Three real, disclosed, dated numbers from the same company, three different results.
Barilliance's own aggregate (2016-2023, methodology and sample size undisclosed) makes an even stronger-sounding claim: back-in-stock emails have the highest open rate of any e-commerce campaign type it tracks, at 65.32% — nearly 70% higher than the lowest performer, post-purchase email. What Barilliance's own page adds immediately after that number, though, is that back-in-stock and post-purchase were "much less effective than the other campaign types" when measured by revenue and conversion — a strong open rate paired with a weak commercial result.
- A specific combo stat — "back-in-stock emails get a 65.32% open rate, 24.49% click-through rate and 14% conversion rate, per Barilliance" — circulates across dozens of listicle-style blog posts. We checked Barilliance's actual, current page directly: the 65.32% open rate is real. The 24.49% click rate and 14% conversion rate appear nowhere on it, and the page's own stated conclusion — back-in-stock underperforms on revenue — cuts against a 14% conversion figure rather than supporting one.
- One real, dated case study exists outside vendor self-reporting: MarketingSherpa documented a back-in-stock alert program at BirkenstockCentral.com that ran a 22.45% conversion rate in the period after its March 2011 launch, with a 30-day snapshot showing a 36.5% open rate, 35% read rate and 26% click-through rate. It's a single retailer from 2011 — an illustration, not a current cross-vendor benchmark.
Back-in-stock software vendor Swym advertises 30-35% click-through and 20% conversion "on alert traffic" on its own product page, with no methodology, sample size or time period disclosed anywhere on the page. That's usable in an article only as a vendor's marketing claim about its own product — not as independent research.
Does WhatsApp or SMS actually beat email at winning back a waitlisted shopper?
Three specific claims explain most of what circulates here, and none of them survived a direct check of their own cited source. A "98% WhatsApp open rate, with 90% read within three minutes" claim, repeated across dozens of sites, traces to a Twilio blog post that attributes the 98% figure to SMS and WhatsApp combined — not WhatsApp specifically — and attributes the "90% within three minutes" figure specifically to SMS, not to WhatsApp at all. A claim that Hellmann's, Adidas and IKEA saw "up to 3x higher recovery rates" after switching to WhatsApp cites "Meta Case Studies / Shopify 2026" — a report that doesn't exist on either company's site; Hellmann's real, documented WhatsApp campaign is a recipe chatbot in Brazil, unrelated to restock or cart recovery, with no published recovery-rate figure anywhere. And a claim that WhatsApp restock alerts convert at 18-25% (versus SMS at 21-40%, email at 5-7%) is attributed to "Sakari SMS marketing benchmarks" — we checked Sakari's own site directly, and WhatsApp appears there only as a "Coming Soon" roadmap item. Sakari doesn't offer WhatsApp messaging yet, so it has never published a WhatsApp benchmark of any kind.
The most rigorous real evidence on channel choice comes from two peer-reviewed randomized controlled trials — neither about e-commerce, both about health-behavior reminders, and both finding the channel mattered far less than marketers claim. Kulhánek et al. (2022, JMIR mHealth and uHealth) randomized 591 lapsed users of a smoking-cessation app to SMS or email reminders: 34.2% of the SMS group and 31.7% of the email group went on to initiate a quit attempt, a difference with no statistical significance (χ² = 0.4, P = .52). A larger, nationwide double-blind trial in Norway (Gram, Larbi & Wangberg, 2019, same journal), randomizing 4,335 smokers to identical cessation content by SMS or email, found six-month abstinence rates of 11.46% and 10.96% respectively — an odds ratio of 1.05, with a confidence interval comfortably straddling 1.0.
- The one real e-commerce data point we could find, from a Kulin-agency guest post on Klaviyo's own blog, is a single client's 90-day back-in-stock numbers — and it splits the difference in an interesting way: SMS drew a 5.3% click rate against email's 1.9%, nearly a 3x gap, but conversion rates came out close: 8.5% for SMS versus 7.9% for email.
Kulhánek et al. 2022 — initiated a quit attempt
Gram et al. 2019 — 6-month abstinence
In Israel specifically, WhatsApp is used by 99% of the population, ahead of YouTube at 97%, per the Israel Internet Association's 2025 index — reach isn't in question for an Israeli audience. What isn't backed by any source we could verify is a specific conversion multiplier for restock alerts. The honest framing, consistent with both real studies above: WhatsApp is worth building as a channel people opted into and prefer, not because a verified percentage says it converts better than email.
Does sending the alert instantly actually beat a batched send?
This is the most fabricated-looking corner of the whole topic. A claim that notifications sent within 15 minutes of restock convert at 25%, dropping to 18% after an hour and 10% after four hours, is attributed to "Klaviyo's 2025 timing analysis" on the page that states it — but no such report exists anywhere on Klaviyo's own site. A separate claim that alerts sent within five minutes convert 45% higher than ones sent an hour later is credited to Omnisend by name on several SEO blogs — but no such report exists anywhere on Omnisend's own site, and none of the pages repeating it link to one. And a bare, uncited line that "every hour of delay reduces conversion by 5-8% as urgency fades" appears with no study, sample or source attached to it at all.
The one real, dated case study on this specific question points the other way. The MarketingSherpa-documented BirkenstockCentral.com program from the section above didn't send instantly — it ran on an automated nightly inventory scan, batching all of that day's restocks into one first-come-first-served send once every 24 hours, capped to available quantity. It still converted at 22.45%.
A vivid real example of true instant-demand dynamics does exist, just not as a notification-speed benchmark: when retailer Antonline tweeted PS5 restock availability at 10:53am ET on February 4, 2021, a shopper reported the entire stock "Gone in less than 10 seconds... wow!" by 10:55am. That's real and dated (Tom's Guide), but it describes bot-driven scalping demand on a console during a global shortage, not how fast a typical restock-alert email or WhatsApp message needs to go out to convert well. The two shouldn't be conflated, and nothing in either case study contradicts a batched send working fine for most products.
Does scarcity messaging actually work, and how should it be worded?
Unlike the timing and channel claims above, the psychology of scarcity has real peer-reviewed research behind it, going back exactly fifty years. In a classic 1975 experiment (Worchel, Lee & Adewole, Journal of Personality and Social Psychology), the same cookies were rated more desirable when a jar held two of them than when it held ten — and the effect was strongest not when cookies were constantly scarce, but when supply visibly dropped from abundant to scarce. Scarcity blamed on high demand rated higher than scarcity blamed on an accident.
What happens when a product goes the other way, into a stockout, depends heavily on how committed the shopper already was. A widely-cited study (Fitzsimons, 2000, Journal of Consumer Research) found that a shopper's reaction to hitting a stockout depends on their commitment to that specific item and how personally the stockout announcement is directed at them: high commitment paired with a stockout that makes the remaining choice harder produces lower satisfaction and more store-switching, while low commitment paired with a stockout that simplifies the choice can land neutral to positive. One specific, actionable detail from the same research: a personalized stockout announcement provokes a more negative reaction than a generic one — the opposite of what you might assume, and a reason not to over-personalize the apologetic "sorry, still out" message even while personalizing the eventual "it's back" one.
How to word the eventual alert also has research behind it, and it isn't one-size-fits-all. Gierl & Huettl (2010, International Journal of Research in Marketing) found that supply-based scarcity signals ("limited edition") work better for products bought partly for status or visibility, while demand-based signals ("almost sold out") work better for functional, non-status products. Separately, Aggarwal, Jun & Huh (2011, Journal of Advertising) found that quantity-based scarcity ("only 3 left") outperforms time-based scarcity ("offer ends in 3 hours") at increasing purchase intention, with the gap widening further for symbolic or status brands — an effect the researchers found was mediated by shoppers' perceived competition with other buyers. And a 2015 study (Zhu & Ratner, Journal of Marketing Research, five experiments) found scarcity doesn't just increase demand broadly — it polarizes choice within a set, pushing shoppers toward whichever item was already their favorite, an effect driven by scarcity-induced arousal.
None of this compresses into one clean multiplier, and the field's own meta-analysis says so directly: a 2022 meta-analysis of 416 effect sizes across 131 studies (Barton, Zlatevska & Oppewal, Journal of Retailing) found scarcity cues reliably increase purchase intent on average, but which type works best depends on the product — demand-based scarcity performs best for utilitarian products, supply-based scarcity for experiences, and time-based scarcity for high-involvement purchases.
What doesn't check out are the specific percentages that circulate on scarcity-marketing listicles: "only X left" messaging boosting sales by up to 226% (sometimes 241%, depending which page repeats it) attributed to a Shopify Commerce Trends Report; a 30% (or, elsewhere, 54%) figure attributed to Baymard Institute; a 332% conversion jump from flash-urgency tactics. We checked one of the most-shared source pages for these numbers directly: it cites no links for any of them, only a numbered source list with no way to verify a single figure — and the number attached to the "same" Shopify claim changes between 226% and 241% depending which page repeats it, a telling sign none of it traces to one real report.
What should you actually build, in what order?
- 1Capture the "notify me" signal at the specific product level via a webhook from the store the moment a shopper opts in — tag the contact with the product (or SKU) they're waiting on, not just a generic "wants updates" tag.
- 2Fire a second webhook from the inventory system the moment stock is replenished, matching it back to whichever contacts are tagged for that specific product — someone waiting on a shirt in blue shouldn't get pinged the moment only red comes back.
- 3Route the alert through WhatsApp first for contacts who opted in and have a connected number, falling back automatically to email for everyone else — treat this as coverage across how people actually check messages, not a proven percentage lift for one channel over the other.
- 4If the restock quantity is limited, cap the flow so only the first N contacts on the list receive the alert, or receive it first — that turns a real supply constraint into an honest scarcity signal instead of an implied one.
- 5If you use scarcity framing in the copy at all, match it to the product: quantity language ("12 left") for everyday, functional items; limited-availability language for status or collectible ones. And keep the restock alert itself warm and personal — unlike an apologetic "sorry, still out" message, nothing in the research says good news backfires from being personal.
In oToK, this is one automation built on two webhook triggers — one from the store's "notify me" widget, one from its inventory system — plus a tag or field-changed condition to match contacts to the right product, a channel router for the WhatsApp-then-email fallback, and a capacity gate for a limited restock quantity. No separate flow is needed per product: the same automation matches whichever product tag fired.
Frequently asked questions
- Do back-in-stock alerts actually outperform other marketing emails?
- By vendor-reported numbers, generally yes — but the specific figures don't agree even within one company. Omnisend's own site lists three different results for the same automation across three pages: open rates of 58.80% and 59.19%, and conversion rates of 5.34%, 6.46% and 6.72%. Barilliance separately reports the highest open rate of any campaign type at 65.32%, while noting in the same report that back-in-stock underperforms on revenue. A specific "65.32% open / 24.49% click / 14% conversion" combo attributed to Barilliance has only the first number real — the other two don't appear on its page.
- Does WhatsApp or SMS beat email for restock alerts?
- Every specific multiplier we checked — a 98% WhatsApp open rate, a 3x recovery lift for Hellmann's/Adidas/IKEA, an 18-25% WhatsApp conversion rate — failed a direct source check; none traces to what it's attributed to. The most rigorous real evidence, two randomized controlled trials outside e-commerce, found SMS and email produced statistically indistinguishable behavioral outcomes. One real single-retailer case saw SMS draw triple the click rate of email but land within a point of it on conversion (8.5% vs. 7.9%).
- Should a restock alert be sent instantly, or is a batched send okay?
- Every specific "send within N minutes for X% more conversion" statistic we checked was fabricated or misattributed, including two separate claims credited to Klaviyo and Omnisend that don't appear anywhere on either company's own site. The one real, dated case study — a back-in-stock program that ran for years — sent its alerts once nightly in a batch and still converted at 22.45%.
- Does "only 3 left" scarcity messaging actually increase sales?
- The underlying psychology is real and peer-reviewed, from a 1975 experiment through a 2022 meta-analysis of 416 effect sizes — but none of it supports a single clean percentage lift. What the research does show: quantity-based scarcity ("only 3 left") tends to beat time-based scarcity ("ends in 3 hours"); which framing works best (limited-edition vs. almost-sold-out) depends on whether the product is bought for status or function; and the specific "up to 226% more sales" style numbers circulating on marketing blogs don't trace to the institutions they're attributed to.
- How much do stockouts actually cost businesses?
- IHL Group's most recent analysis puts the worldwide cost of "inventory distortion" at $1.77 trillion in 2023 ($1.2 trillion from out-of-stocks alone). The commonly repeated "$1.75 trillion" figure is a different, older (2015) number that bundles preventable returns and overstocks in alongside out-of-stocks — not a current, pure-stockout statistic. Separately, Baymard Institute's usability research found 68% of e-commerce sites won't even let a shopper order a temporarily out-of-stock item, and 30% of shoppers say they'd abandon the site immediately when they hit one.
