A klaviyo back in stock flow sells to people who already told you they wanted the product. They found it, could not buy it, and handed over an email address so you could tell them when it came back.
You can consider these people the hottest of hot leads as they’re literally waiting to buy. When the alert lands they move fast, because missing it twice is the outcome they want to avoid.
Given all that intent, building the flow turns out to be the easy part. What goes wrong with restock alerts is that they misfire in silence for a couple of different reasons, which we are about to dive into.
Why should you listen to us? Because we are Email Kong, a specialist Klaviyo agency that has been awarded master platinum status by the platform - meaning we’re one of the very best.
Here’s how our agency approaches back in stock flows.
How To Set Up A Back In Stock Flow In Klaviyo
Building a klaviyo back in stock flow is a short sequence of decisions, and each one narrows the pool of people your alert can still reach. The last decision matters most. It sets how much of your waitlist hears from you at all.
Check Your Shopify Integration Before You Build The Flow
Open the integration before you open the flow builder. A restock alert reaches into your catalog for the product and into purchase history for the person, and it does both in the seconds after stock lands.
Both of those lookups depend on the sync. Manual sends do not scale, automated systems do, and that only holds when the data feeding them is complete.
There is a catch. Klaviyo's Shopify integration needs more than recent orders. Historical purchase data and customer tags feed the segmentation every automated flow depends on, and for a restock alert that is what tells you which people on the waitlist have bought from you before.
Run a partial sync and your restock alert cannot reference past purchases. It cannot tell a repeat customer from someone who has never bought anything. You lose the ability to treat those two people differently before writing a word of copy. Our guide to connecting Klaviyo to Shopify covers what a complete sync includes.
Create The Flow And Set The Trigger
With the data in place, the flow itself is quick. Klaviyo's help documentation is explicit that when someone subscribes to a restock alert, a Subscribed to Back in Stock event is tracked on their Klaviyo profile, and that event is what triggers the flow.
Restock a product nobody subscribed to and nothing sends, however much stock lands. The first message has one job. It moves a shopper who already decided they wanted this product back to the product page.
That one job is worth more than it sounds. According to Klaviyo's published 2026 email benchmarks, flows generate nearly 41% of total email revenue from just 5.3% of sends.
Klaviyo puts revenue per recipient on those flows at nearly 18 times what a broadcast send returns. Restock alerts sit at the sharp end of that spread, because nothing else in your flow stack goes to someone who asked for that exact product by name.
Across the accounts we manage it is routinely the highest revenue-per-recipient flow on the account.
Choose Your Minimum Inventory Number
Slow down here. This is the setting that decides your reach.
Your restock minimum sets how many units must be in stock before Klaviyo sends anything, and the obvious reason to use it is to stop yourself announcing five units to a waiting list of five hundred people who will mostly arrive to find it gone.
The setting also keeps applying while the send is running, which is what catches people out. Klaviyo's own community team has put it plainly. A back in stock flow keeps sending to the profiles who subscribed until inventory drops below the minimum required to notify them. Set that minimum at 10 and anybody still queued stops receiving the email once availability falls under 10.
Read it as a stop condition. One merchant posting on the Klaviyo Community forum found that during a real restock of more than 500 units, most of the waitlist never heard from them at all. Nothing was suppressed. Inventory had sold through the threshold while the queue was still moving.
Knowing that, set the number against your real restock depth. Bring in 40 units that sell in a day and a minimum of 25 will strand most of your list. A low single-digit minimum reaches more people and risks a few clicks landing on a sold-out page. Make that trade deliberately, and make it per product. One number for the whole store will fit almost none of it.
Notify Subscribers In Batches Or All At Once
Your threshold does not work alone. Klaviyo's delay component controls how the queue is released, so you can notify subscribers in staggered groups. That keeps your site standing when a popular item lands.
Batching interacts with the setting above, and the combination is what catches stores out. Subscribers in later groups are the most exposed to your threshold, because stock has had longer to sell before their turn comes around.
Batch a popular restock too slowly and you have built something that reliably tells your most patient subscribers last. Sometimes it never tells them at all.
Send The First Email Within Minutes
Everything above comes down to how fast the first message goes out. A shopper who waited for this product has not stopped shopping, and the ones who find it somewhere else first are gone for good. Every hour between stock landing and the alert going out is revenue leaving through a door you opened.
Klaviyo has improved its side of that. In August it shipped Flows 2.0, a rebuilt processing engine for high-volume flows, and the release notes put its throughput above 74,000 profiles per second.
For most stores that removes the queue as an excuse. Whatever delay remains between stock landing and your subscribers hearing about it is now yours to close.
So what remains is operational. Somebody marks the stock as received, and the flow needs to be live and tested before they do it.
Klaviyo's release notes also describe Flows Analyst, shipped in August. It scores your welcome, browse abandonment, cart abandonment and winback flows against Klaviyo's own platform-wide figures. Restock is not in that set yet, so the number you compare against is still your own last restock.
How To Set Up Back In Stock Alerts For Product Variants
Shoppers do not subscribe to products. They subscribe to a size, a color, a scent or a capacity.
Klaviyo records which one, because the subscription happens at variant level and the event carries that variant with it. Most setups discard the detail, and that is a mistake.
When the alert goes out announcing the product, your shopper clicks through hoping for the medium in navy, and finds the extra large in red. You have spent the one message they were waiting for on an item they already rejected.
Two changes fix it. A dynamic product block pulls the product information for the item the profile subscribed to, so the email shows the specific thing the shopper asked about, and our Klaviyo email templates guide covers the build.
Then check that your product page lets a shopper pick the variant before the form appears. Klaviyo's own troubleshooting documentation is clear on the cause. Where a theme renders the button against the parent product, or drops the product once every variant sells out, the variant is never recorded.
One caveat before you ship either change. Klaviyo's template builder works differently from the editors in Mailchimp or Omnisend, and untested templates break on mobile.
Treat all of this as integration work. Keeping Klaviyo talking properly to your wider Shopify setup is what holds variant data accurate inside the flow, and that sync drifts after a theme update.
Setting up an apparel client's tech stack means connecting Klaviyo to the whole Shopify ecosystem so the catalog the flow reads matches the catalog the shopper sees. Variant accuracy is downstream of that work. Re-test it after any theme change.
How To Add The Notify Me Button To Your Product Pages
No signup, no send. That makes the button the one component in this whole article you cannot compensate for elsewhere, and Klaviyo's no-code back in stock forms for Shopify and BigCommerce have at least taken theme code out of the install. What they have not fixed is the button failing silently, and our guide to Shopify email automation covers the wider setup this sits in.
Sold-Out Products Hidden From Collections Collect Nothing
Plenty of stores hide sold-out products to keep collection pages looking full, which is a reasonable merchandising instinct. It also switches off your demand capture.
The reason is simple enough. A shopper who cannot reach the product page cannot join the waitlist. Push sold-out items to the bottom of the collection instead, where they stay reachable and keep collecting intent. Theme-level behavior needs the same check, because a theme that drops a product once every variant is sold out removes the page your form sits on.
Continue Selling When Out Of Stock Blocks The Button
This one catches almost everybody once. Klaviyo's community documentation is blunt about it. With that setting enabled the Notify Me button and its form never appear, and no alert is ever sent. How carefully you built the flow behind it makes no difference.
Klaviyo needs the product marked unavailable to know there is anything to notify about. Using that setting to take backorders is a legitimate choice, and it means choosing backorders over a waitlist. Decide it on purpose. Reports of the button missing on some products, or missing once a variant is selected, almost always trace back to the theme.
One more thing to check while you are in there. A restock alert that lands in spam is worth nothing, and we hold a 70-plus deliverability score across the accounts we manage by testing inbox placement rather than assuming it. A sudden burst of sends to a segment that has been dormant for months is exactly the pattern that gets filtered.
How To Collect More Emails And Phone Numbers For Restock Alerts
A restock waitlist is a list-growth asset. Treating it as one changes what it is worth to you.
Most of the people on it have never bought from you. That makes the waitlist a first-purchase channel as much as a recovery one, and it deserves the same attention you give any other capture point on the store.
The numbers back that up. Nearly 48% of flow-driven email revenue comes from new buyers, against 16% from campaigns, according to Klaviyo's published 2026 benchmarks. A restock waitlist is mostly new buyers by construction, so we treat it as list growth.
Put The Signup Where Shoppers Already Are
Your sold-out product page only catches shoppers who found the item. Plenty never get that far.
Add capture where demand already shows itself. Collection pages where an item is greyed out work well. Search results that return nothing work just as well, because a shopper searching for something you do not have is telling you what they wanted in their own words.
Post-purchase touchpoints are the third place worth building, and our browse abandonment guide covers the earlier version of this same intent. Branded tracking pages pull repeat visits from people who have already bought once, and those visits convert to opt-ins at a rate cold traffic never matches. We test popups and lead captures across the store for the same reason we test anything, which is that placement decides more than copy does.
Switching the flow on late does not waste what you collected. Profiles who subscribed beforehand can be added to the flow retroactively, so an existing waitlist is never stranded.
Collect SMS And WhatsApp Consent On The Same Form
Since February 2026 the back in stock form takes WhatsApp consent alongside SMS and email in one step. One signup, three channels, no extra friction.
That matters more here than on most forms, because speed decides the sale. A text landing the moment stock returns beats an email waiting for the next inbox check. Subscribers who give you two channels are worth materially more than those who give you one.
Two obligations come with it. Capture consent cleanly, because importing or merging contacts without checking consent status puts you at risk under GDPR and the CAN-SPAM Act. Then keep the list clean, because Klaviyo prices on active profiles and a waitlist nobody prunes turns into a standing cost.
Give Your Best Customers Early Access Before Everyone Else
Once your klaviyo back in stock flow works, you get to choose who hears first. Stores treat that as a scheduling detail. It is worth more than that.
A real back-in-stock email we built for GrubTerra.
Sending that kind of announcement to a chosen group first is a supported setting. Klaviyo's notification rules set how many subscribers are notified per restock and in what order, so a restock can go to one group before another. What you do with that is a loyalty decision.
Made deliberately, that decision is a relationship statement. Early access tells your best customers that being on your list means something real, and it costs nothing but sequencing.
That is how we built the Alma de Ace Coca-Cola collaboration. Subscribers got a password for genuine early access ahead of the public launch. Inventory was moving within minutes of the list going live, and Alma de Ace's campaign returned 57% attributed revenue from Klaviyo.
Per that same case study, it also returned a 213% increase in returning-customer revenue. Early access converts the drop and changes what the customer does afterwards.
A restock is that event at a smaller scale. Run the first batch to customers who have ordered before, then open it to the rest an hour later. What changes is who feels rewarded for having waited.
Where A Klaviyo Partner Fits In
Read back over the four failures above and you will notice none of them announces itself. The flow reports as sent, the subscribers report as notified, and the button looked fine on the one product page anybody checked.
Finding that class of problem is what an audit is for. On a restock flow we check three things the dashboard will not show you.None of that comes with an obligation. Take what the audit finds and fix it yourself if you prefer.
That work is most of what we do. Across the accounts we manage we have built the retention systems behind $58.2M in attributed revenue, and fixes like these surface in week one of our 8-Week ROI Timeline, where the foundation work alone tends to return two to three times.
If your klaviyo back in stock flow has been live for months without anyone confirming how much of the waitlist it reaches, start there. Get your free Klaviyo audit and we will show you what it is doing. Our email marketing audit guide explains what we look at.
The same discipline applies to the flows either side of a klaviyo back in stock flow, and our guide to abandoned cart recovery covers the nearest of them.