Themivo
You collect back in stock sign-ups every week, but when the product returns, sales barely move. The most likely cause is the setup, not the idea: a restock of a few units goes to every subscriber at once and sells out before most of them act, or a setting quietly holds the alert back. Start by checking how many units trigger your alerts and whether every alert message is live and actually sending.
Why back in stock alerts don't bring customers back
Back in stock alerts usually underperform because of how they are configured, since the format itself tends to convert well when it works. In Omnisend's email marketing benchmarks, product back in stock automations had a 6.72% conversion rate and $9.14 in revenue per email in 2025, the highest of the automation types listed, while Omnisend's statistics page gives 6.46% for the same year. Read that as roughly 6 to 7%, with limits: it is one vendor's data from its own merchants, it is an average across thousands of stores, and the people who receive these emails have already said they want the product. Omnisend's 2025 ecommerce marketing report defines conversion rate as attributed orders compared to total messages sent.
No independent study explains why one store's alerts fail. The causes below come from Klaviyo's and Shopify's help documentation, plus practical reasoning where the docs stop, and we say which is which.
Small restocks sell out before most subscribers act
A restock of only a few units often sells out before most subscribers open the email. Klaviyo's guide to building a back in stock flow says that by default all subscribers are notified at once when an item is restocked. Shopify Flow's Product variant back in stock trigger fires when a variant's inventory goes from 0 or less to 1 or more, so a single returned unit counts as a restock. If hundreds of people signed up and four units came back, most of them meet a sold-out page again, which can teach them to ignore your next alert.
Follow-up emails arrive after the item sold out again
A second or third alert can land after the product is gone again. Klaviyo's article on how back in stock flows work says that after the initial message is sent, Klaviyo cannot check the inventory to see whether the item has gone out of stock again. A reminder sent later can point shoppers to an empty product page.
Alerts go out late or never go out
Some back in stock alerts are delayed or silently blocked by settings. Klaviyo advises turning Smart Sending off for the alert so everyone gets it, and notes that messages left in Draft will not send. Batched sends, which Klaviyo offers, wait between batches by design, so later subscribers hear about the restock after earlier ones. If you send SMS alerts, check Klaviyo's help center on how quiet hours affect timing.
Store stock is counted as online stock
If you sell in person with Shopify POS, an alert can fire for stock that online shoppers cannot buy. Klaviyo's build guide says that with POS hardware and an online store, the back in stock flow counts all inventory in your physical store as well as your warehouse. Nobody has measured how often this happens, but one false alert is enough to frustrate a keen shopper.
Old sign-ups never get an email
Shoppers who signed up before your flow went live may never be contacted. Klaviyo says adding past profiles to a back in stock flow typically won't bring in new people, and recommends sending a campaign to the people in the back in stock report instead.
The email is generic and makes the shopper work
An alert that only announces the restock and links to the product page adds steps between interest and purchase. We found no study that measures the effect of a direct checkout link or a discount code in back in stock emails, so treat this as reasoning: every extra tap (choose the variant again, add to cart, open the cart) is another chance to lose a shopper reading on a phone.
Guests signed up without an email address
Some sign-ups can't be emailed at all. Many wishlist and notify tools let guests save or follow a product without an account, and a guest with no email address can't receive an alert. No data shows what share of sign-ups this loses, but if your tool counts guest saves next to email sign-ups, your reachable audience may be smaller than the number you see.
How to tell which one is hurting your store
Comparing sign-ups, alerts actually sent and units restocked each time will usually point to the cause. Work through these checks:
- Compare units restocked with subscribers notified. If you regularly notify hundreds of people for a handful of units, small restocks are the problem.
- Confirm the products have Inventory tracked turned on in Shopify, since the Flow back in stock trigger needs it.
- In Klaviyo, open the alert message and confirm it is Live, not Draft, and that Smart Sending is off. The back in stock settings tab only appears after at least one sign-up has been recorded.
- Count how many messages the flow sends. Klaviyo says one message is usually enough.
- If you use Shopify POS, check which inventory locations feed your alert tool.
- Compare the size of your back in stock report with the number of people who received alerts. A big gap suggests old sign-ups were never reached.
- Open your alert email on a phone and count the taps from the email to checkout.
Cause | Sign | Fix |
|---|---|---|
Small restocks | Product sells out soon after alerts | Restock minimum, batching, low stock alert |
Late follow-ups | Clicks land on sold-out pages | Send one alert |
Blocked alerts | Sign-ups but few or no sends | Smart Sending off, message Live |
POS stock counted | Alerts for stock not sold online | Check inventory locations |
Old sign-ups | Report bigger than recipient count | One-off campaign |
Generic email | Clicks but few checkouts | Buy now link, optional discount |
How to fix it
Use an alert tool with Buy now links and low stock alerts
Themivo Wishlist & Alerts is a free Shopify app that sends back in stock, low stock, price drop and wishlist reminder emails, each with a Buy now link that opens checkout with the variant already in the cart. Disclosure: we make this app.
Themivo Wishlist & Alerts tackles several causes above in one place, and every feature is included with no paid plans or plan limits:
- Back in stock and low stock alerts, with a low stock threshold you set from 1 to 1000 units, so shoppers hear when only a few are left.
- Editable email templates with a Buy now link and an optional discount code.
- Emails sent by Themivo's mail service with no setup, or from your own SMTP server.
- Alerts sent to Klaviyo and Omnisend as events, plus six Shopify Flow triggers including back in stock, low stock and price drop.
- Analytics for wishlist adds, add to cart rate, orders and wishlist revenue with an attribution window from 1 to 90 days, so you see revenue rather than counts.
- An appearance editor with live preview that fits Online Store 2.0 themes without code edits.
Two things to know: Themivo Wishlist & Alerts launched in October 2026, so it has few reviews so far (5.0 from 5 reviews), and alerts go to signed-in customers because guests have no email address. If you are weighing it against other tools, see our wishlist app comparison and our look at Amp Back in Stock & Preorder vs Notify! Back in Stock.
Set a restock minimum or batch your sends
A restock minimum stops alerts from going out for one or two units. Klaviyo's Restock minimum sets how many units must be in stock before any alert is sent. You can also batch: Klaviyo notifies a set number of subscribers per restocked unit, then waits. In Klaviyo's example, 20 units with customers to notify set to 5 means the oldest 100 subscribers get the alert first. If more stock arrives during the wait, no extra emails go out until the wait ends, so keep the wait short enough that later subscribers aren't left out. Klaviyo's reasoning is simple: if one item is restocked, you don't want to email everyone for that single item.
We would also tell shoppers how many units are left, through low stock wording or a low stock alert. No source tests this, but honest scarcity sets expectations and gives a shopper a reason to act now.
Send one alert, not a sequence
One back in stock message is usually enough, according to Klaviyo, and it needs no time delay. Because Klaviyo can't recheck inventory after the first send, every follow-up risks pointing to a sold-out page. If you want a reminder, use a tool or workflow that checks stock before sending it.
Clear the settings that hold alerts back
Turning Smart Sending off and setting the message to Live fixes the most common silent failure in Klaviyo. Then confirm Inventory tracked is on for every product that collects sign-ups, and review your SMS timing settings if you send texts.
Check inventory locations if you use POS
If your alert tool counts store and warehouse stock together, it can announce a restock that online shoppers can't buy. Review how your locations feed the alert, and check Shopify's help center for how inventory locations work on your plan.
Reach old sign-ups with a one-off campaign
A single campaign to everyone in your back in stock report reaches the people a new flow will skip. Send it only for products that are in stock now, with a clear link to the variant they wanted.
Add a Buy now link and test an optional discount
A direct checkout link removes the steps between the email and payment. No data shows that a link or a discount raises recovered sales, so test it: add a Buy now link to every alert, try a discount code on a few slow products only, and compare orders over the same attribution window.
Get guests to sign in before they follow a product
Asking guests to sign in turns an anonymous save into someone you can email. In Themivo Wishlist & Alerts, a guest's wishlist moves to the customer account at sign-in, and Sign in with Shop keeps the list on every device.
Add Klaviyo or Flow follow-ups for the rest
Shopify Flow's back in stock trigger can handle store tasks, while your email tool handles shoppers. The actions listed on Shopify's trigger page are product and variant actions such as tags, collections, metafields and publishing; an email action to customers is not listed there. Use Flow to republish a product or update a collection on restock, and send the alert itself from an app or from Klaviyo or Omnisend.
Frequently asked questions
What is a good conversion rate for back in stock emails?
Omnisend's 2025 data puts back in stock email conversion at roughly 6 to 7% of emails sent: 6.72% on its benchmarks page and 6.46% on its statistics page. These are averages from one email platform's own merchants, so use them as a rough reference rather than a target. If you are far below, check restock size and send settings first.
How many back in stock emails should I send?
Klaviyo says one back in stock message is usually enough, with no time delay. Klaviyo also notes it cannot recheck stock after the first message, so later emails can reach shoppers after the item has sold out again. Its general advice is to keep flows to one to three messages.
Should back in stock emails include a discount code?
No published data shows that a discount in a back in stock email raises recovered sales. These shoppers already want the product, so a discount may not be needed for most items. If you try one, test it on a few products and compare orders against alerts without a code.
Can Shopify Flow send back in stock emails on its own?
Shopify Flow has a Product variant back in stock trigger that fires when inventory goes from 0 or less to 1 or more, but the actions listed on that trigger's help page are product and variant actions, not customer emails. Most stores pair Flow with an alert app or an email platform. Themivo Wishlist & Alerts adds its own Flow triggers and sends the emails itself.
Why didn't my Klaviyo back in stock alert send?
The most common reasons are a message left in Draft, Smart Sending turned on, or a restock below your restock minimum. Klaviyo's settings tab for back in stock only appears after at least one sign-up has been recorded. Also confirm that Inventory tracked is on for the product in Shopify.
What to do first this week
Pick your three most-requested out of stock products and check one thing for each: how many units come back compared with how many people get the alert. Then set a restock minimum or batching, make sure the alert is Live with Smart Sending off, and add a Buy now link. If you want back in stock, low stock and Buy now emails in one free app, install Themivo Wishlist & Alerts from the Shopify App Store.
