A product sells out and the listing stays up. Shoppers keep arriving from search, from ads, from the wishlist they saved months ago, and every visit ends at the same dead end: no add to cart button, no way to leave an email, no record that the demand was ever there. Back in stock alerts exist to catch that moment, and on Shopify the cleanest version runs through Klaviyo.

The idea is straightforward. A shopper who finds a sold-out item leaves their details instead of leaving the store, and when the item is back they get one timely message. The sale that slipped away on the day it sold out happens a few weeks later, and the store learns exactly how many people wanted the thing before it restocked.

This guide covers back in stock alerts with Shopify and Klaviyo end to end: the notify me form, the flow that waits for restock, the SMS layer for fast-moving drops, and the test that keeps the first real sell-out from exposing a broken setup. You need a Shopify store, a Klaviyo account and a browser. Everything here happens in the two admin areas you already pay for.

What a back in stock alert does when a product sells out

Once you publish a back in stock form, Klaviyo automatically shows a Notify me button on any product page where inventory is out of stock, and it removes the button again when stock returns. No developer needed, no snippet to reinstall after every theme change, which is why Klaviyo documents it as the standard path for Shopify stores. When a shopper submits the form, Klaviyo logs a Subscribed to Back in Stock event, and that event is what starts the restock flow (Klaviyo's back in stock form guide).

From there the sequence runs itself. A subscriber enters the flow and waits at a step called the back in stock delay until their exact item restocks. When inventory crosses back to available, they move to the next step and receive a single notification, usually one email or one SMS (Klaviyo's guide to building a back in stock flow). The message is deliberately a one-shot alert, because the job is to say the item is available again, then get out of the way (Klaviyo explains how back in stock flows behave).

Two details make the whole thing work. The alert email builds its product image, title, link and price from your catalog at send time, since an item can restock weeks or months after signup and the listing will have changed (Klaviyo's back in stock email configuration guide). And the notification must have Smart Sending switched off, because Smart Sending exists to ration marketing messages per person per window, and a restock alert that gets rationed away defeats the point (how Smart Sending works in Klaviyo).

The trigger also depends on Shopify reporting the truth about stock. Shopify only treats an item as out of stock when inventory tracking is switched on for that product and the level sits at zero or below (Shopify's documentation on out of stock products). Klaviyo's back in stock feature does not work with the Continue selling when out of stock setting, which is the oversell option Shopify offers for preorders and backorders. If that toggle is on, there is no sold-out state for the button to react to.

Prerequisites: tracked inventory, a Klaviyo account and SMS consent

Before the first step, gather these prerequisites and you can finish the whole setup in an afternoon. A flow, for clarity, is a sequence of automated messages that a single event starts; a trigger is that event; consent is the permission a shopper gives before you contact them. The terms come up again below, spelled out where they first appear.

On cost: Klaviyo's free plan includes up to 250 active profiles, 500 email sends per month and USD 5 of mobile messages per month, with the Shopify integration included (Klaviyo's pricing page, AU version). A small store that sells out a handful of products a month stays inside those limits comfortably. The moment restocks get frequent, the send volume decides when a paid tier makes sense.

Step 1: Add the notify me form to sold-out products

Klaviyo ships a dedicated back in stock form template, and the form itself is the piece that turns a dead product page into a capture point.

Create the form from the back in stock template

In Klaviyo, open Forms and create a new form using the back in stock template. The form collects an email address by default, and once SMS is enabled in your account it can collect a mobile number as a separate opt-in field as well. Klaviyo allows one back in stock form per account, so this single form covers every product in the store (Klaviyo's back in stock form guide). Keep the form copy short: the shopper is already convinced, they just need a place to leave their details.

Set the button placement and publish

Klaviyo gives you placement options for the Notify me button, typically replacing the add to cart area on sold-out products or sitting just below it. Pick whichever your theme renders cleanly, style the button to match the store, then publish. From that moment the button appears automatically on product pages where inventory is out of stock and disappears again when the item is back, with no manual switching between the two states (Klaviyo's back in stock form guide).

Confirm Shopify reports the product as sold out

The button only shows where Shopify says the stock is gone, so three settings need to line up. Inventory tracking must be on for the product or variant, the quantity must be at zero or below, and Continue selling when out of stock must be off (Shopify's out of stock documentation). One more trap: some themes or apps hide sold-out products from the storefront entirely, and a hidden product has no page for the button to live on. If you auto-hide out of stock items, the waiting list never gets the chance to form (Shopify's guide to hiding out of stock products).

Step 2: Build the Klaviyo back in stock flow

The form captures the demand. The flow is what delivers on it, and it has a shape that differs from every other marketing flow you will build, so it is worth going through the pieces in order.

Create the flow and wire the trigger

In Klaviyo, open Flows and create a flow from the back in stock template, or start blank and choose the Subscribed to Back in Stock metric as the trigger (Klaviyo's back in stock flow builder). Set the flow status to Live or Manual before signups start arriving; a flow that is still a draft does not accept subscribers into the waiting list (Klaviyo's explanation of back in stock flow behaviour).

Add the back in stock delay and the single alert message

Drag in a back in stock delay as the first step after the trigger. Every subscriber waits at this step until their exact item restocks, which means someone who signed up for a medium waits for the medium, not for the whole product. When the item is available again, the flow moves them forward (Klaviyo's back in stock flow builder).

Add one message after the delay. Email is the default, and the message block pulls the product image, title, URL and price from your catalog at send time, because an item can restock weeks after signup and the listing may have changed (Klaviyo's back in stock email guide). Switch Smart Sending off on this message. Smart Sending stops a profile from receiving too many marketing messages in a window, and when a restock alert is the one message that matters, rationing it away loses the sale (Klaviyo's Smart Sending documentation).

Set minimum inventory and customer notification rules

Two controls stop the flow from over-promising. A minimum inventory rule makes the flow wait until a restock reaches a usable quantity, so a box of three units does not trigger an alert to three hundred people. Customer notification rules cap how many people get notified per restocked unit. Klaviyo's example: 20 units restock, the rule allows 5 customers per unit, and the oldest 100 subscribers on the list get the alert (Klaviyo's back in stock flow builder). Everyone else stays queued for the next batch, which keeps the promise in the email honest.

Step 3: Turn on SMS so urgent restocks reach phones

Email works, but an inbox can sit unopened for a day. Klaviyo states that text messages are typically read within three minutes, which makes SMS the better channel when the restock will sell through fast (Klaviyo's guide to SMS in back in stock flows). If you want the channel-by-channel argument, we compared Klaviyo SMS versus email for ecommerce revenue in a separate post.

Enable SMS and register a sending number

SMS starts in account settings, not in the flow. Open Settings in Klaviyo, turn on SMS, and follow the prompts to claim a sending number. In Australia, branded sender IDs require verification or registration before they can send, so leave a few days for that step if you want your brand name as the sender (Klaviyo's SMS setup guide).

Add the consent split so SMS goes to the right people

Back in the flow, place a conditional split after the back in stock delay. Profiles with SMS marketing consent take the SMS path and get the text alert; everyone else continues down the email path. Klaviyo recommends limiting SMS in the flow to one or two messages, and with a restock alert one is normally enough (Klaviyo's SMS in back in stock flows guide).

Put disclosure language on the signup form

If the form collects a mobile number, it needs disclosure language above the SMS opt-in. Klaviyo is blunt about this: disclosure is legally required wherever SMS consent is collected, and it must name the service, message frequency, how to opt out with STOP, and where to find your terms and privacy policy (Klaviyo's SMS disclosure guide). Klaviyo provides default wording you can edit, and this is the one field on the form you should not trim.

Step 4: Test the whole flow before the next sell-out

A back in stock flow has more moving parts than a welcome series, and each part can fail silently. Run the full loop on a real product before you rely on it during an actual sell-out. The eligibility rules and this test routine apply to every back in stock tool, not just Klaviyo (the setup checklist in Notify Me's help centre).

Subscribe as a shopper would

Pick a product, set its inventory to zero in Shopify admin, and open your store in an incognito window so Klaviyo does not recognise you as a contact. Visit the product page and confirm the Notify me button appears, then submit the form with a test email address. Back in Klaviyo, confirm the Subscribed to Back in Stock event logged and the profile entered the flow.

Restock in Shopify admin and watch the alert send

In Shopify admin, raise the product's inventory from zero to a positive number. Within a short window the profile in Klaviyo should move out of the waiting state and into the sent step, and the alert should land in the test inbox (Klaviyo's explanation of flow states). Open the email and check the product image, price and link, since those come from the catalog lookup and are the parts most likely to be wrong (Klaviyo's back in stock email guide).

Check the queue and repeat the loop

While you are in there, look at the waiting list itself. In the flow, open the back in stock delay and choose View back in stock reports, where Klaviyo can export the currently queued subscribers as a CSV with the email, date added, product and variant (Klaviyo's guide to exporting queued back in stock subscribers). Then run the same test on a second product with a variant, such as a size, to confirm variant-level signups behave. Two clean runs and the flow is safe to trust.

How to measure back in stock alerts: waiting list size, conversion and recovered revenue

Once the flow is live, the waiting list becomes one of the more readable demand signals in the store. The CSV export shows which products and variants people are queued against and how long they have waited, which is a direct answer to the question of what to reorder deeper (Klaviyo's queued subscriber export guide). A product with 400 people waiting justifies a bigger purchase order than one with 12.

On conversion, the honest position is that the number depends on whose data you read. Omnisend's 2025 ecommerce data puts back in stock signups at a 6.46 percent conversion rate, the highest of any automation type in its report, with back in stock emails at 58.03 percent open rates, 21.19 percent click rates and a 30.5 percent click-to-conversion rate (Omnisend's back in stock setup guide with its 2025 figures). Ecommerce agencies that specialise in Klaviyo report a similar band: open rates above 60 percent on the alert email, click rates of 15 to 25 percent and conversion rates of 5 to 12 percent (Purposeful Profits' analysis of back in stock flow performance). Treat those as directional. Your own flow report in Klaviyo will settle the number for your store within a few restocks.

Klaviyo also publishes flow benchmarks aggregated across thousands of customers in different revenue bands, which is the reference Klaviyo itself points to when judging a flow's revenue contribution (Klaviyo's flow email benchmarks). Its benchmark tables cover abandoned cart, post purchase and welcome flows rather than back in stock, so compare your flow's revenue per recipient against your store's other flows instead of chasing a published back in stock figure that does not exist.

The metric that ties it together is recovered revenue: sales that arrive from the alert after the item was unavailable. Klaviyo attributes those orders to the flow, and the number sits next to the list size in your flow report. It belongs in the same weekly review as the other demand-capture numbers, which is why we wrote a companion guide on AI cart recovery for Shopify and Klaviyo for the carts that almost happened, and one on win-back flows for buyers who go quiet after they do purchase. Stockouts, abandoned carts and silent lapsers are the three leaks in one funnel, and each has its own flow.

Frequently asked questions about back in stock alerts

Why is the notify me button not showing on my sold-out product?

The product is probably not being reported as sold out. Shopify only treats an item as out of stock when inventory tracking is on and the level is zero or below, and Klaviyo's back in stock form does not work when Continue selling when out of stock is enabled. A theme that hides sold-out products also removes the page the button would sit on.

Can shoppers waitlist one size or colour instead of the whole product?

Yes. Signups are recorded per variant, so a shopper who wants a medium waits for the medium to restock, and the flow releases each subscriber when their exact item comes back. The waiting list export shows the variant level of demand for every product.

How long do people wait before they hear back?

Until that item restocks. The back in stock delay holds every subscriber until inventory crosses back to available, which can be days, weeks or months depending on your supply. The alert email looks up the product at send time, so the price, image and link stay current even after a long wait.

Should restock alerts go by email or SMS?

Email reaches everyone on the list. Klaviyo notes that text messages are typically read within three minutes, so SMS suits time-sensitive restocks where stock will move fast. Run a split that sends SMS to people who gave consent and email to everyone else, and cap SMS in the flow at one or two messages.

What happens if I restock a small batch and hundreds are waiting?

Set a minimum inventory rule so the flow only fires once stock is at a usable level, and set customer notification rules that cap how many people get told per unit. Klaviyo works through an example where 20 units restock with 5 customers notified per unit, which alerts the oldest 100 subscribers so the message never promises more than the shelf holds.

Does Shopify have a native back in stock option?

Shopify Flow ships templates that email waitlisted customers when a product comes back, and the Shopify App Store lists dedicated back in stock apps. The Klaviyo route adds the automatic notify me button, SMS and live product details in one place, which is why it is the common choice for stores already on Klaviyo.

Set up your first back in stock alert this week

Start with one product that sells out regularly. Publish the form, build the flow, decide on SMS, run the test loop, and leave the flow on for the next sell-out. Within a restock cycle you will have a waiting list size, an alert conversion rate and a recovered revenue figure for that one product, and those three numbers tell you whether to roll the setup across the catalog.

This is the kind of system we build at Supernodes. The pilot starts with an audit of the store, connects Klaviyo, launches the flow and measures recovered revenue on the first restock. If a sell-out week is costing you sales, speak with us.