Back-in-Stock Notifications: The Highest-Converting Flow You're Probably Not Running

A customer visits your product page. The item is out of stock. They leave. In most Shopify stores, that's where the story ends. The demand existed. The intent was there. But the product wasn't available, so the revenue disappeared.

Back-in-stock notifications capture that demand and convert it automatically when inventory returns. The subscriber has already told you exactly what they want. When you notify them that it's available, you're delivering exactly the message they asked for. This is why back-in-stock flows consistently have the highest conversion rates of any automated flow in Klaviyo.

The setup requires two components. First, a back-in-stock signup form on your product pages. When a product is out of stock, the "Add to Cart" button should be replaced with (or accompanied by) an email capture field: "Notify me when this is back." Klaviyo's back-in-stock feature integrates with Shopify to automatically show this form when inventory hits zero and hide it when stock returns.

Second, the flow itself. Klaviyo triggers the back-in-stock flow when a previously out-of-stock product's inventory goes above zero. The flow sends to everyone who signed up for that specific product's notification. The trigger is automatic — no manual campaign needed.

The first email should fire quickly. Within minutes of restocking, not hours. These subscribers have been waiting. The faster you notify them, the higher the conversion rate. Delay by 24 hours and some will have found an alternative or lost the impulse.

The email content should be direct and product-focused. The subject line leaves no ambiguity: "[Product Name] is back in stock" or "The [product] you wanted is available again." The body shows the product image, name, price, and a prominent CTA button linking directly to the product page. No distractions, no cross-sells in this first email, no lengthy copy. The subscriber knows what they want. Get them to the product page as fast as possible.

Add urgency if it's genuine. If the product sold out quickly last time, say so: "This sold out in 48 hours last time." If inventory is limited, mention it. But don't fabricate scarcity — subscribers who signed up for a notification are engaged enough to notice if the product is still available weeks later despite "limited stock" claims.

A second email 24 hours later targets subscribers who opened the notification but didn't purchase. This follow-up can add social proof ("Rated 4.8/5 by X customers"), customer photos or UGC, and a more detailed value proposition. If margins allow, a small incentive (free shipping or 10% off) can convert hesitant subscribers. But many brands find the second email converts well without a discount because the intent is already high.

A third email is usually unnecessary. If someone didn't buy after two back-in-stock notifications, they've likely moved on. Sending a third risks being annoying rather than helpful.

The technical setup has some nuances. Klaviyo's back-in-stock feature works best when your Shopify product catalog is fully synced. Verify this in Klaviyo > Content > Products. If products have variants (size, color), the notification should ideally be variant-specific: if someone signed up for the Blue Medium, notifying them that the Red Large is back doesn't help. Klaviyo handles variant-level tracking when properly configured.

For brands with frequent inventory fluctuations, add a filter to prevent notifications for products that briefly flicker in and out of stock. A condition like "inventory quantity is greater than 5" (rather than just greater than zero) prevents premature notifications for products that might sell through the small restock immediately.

The back-in-stock flow also serves as a demand signal for inventory planning. If you're consistently seeing hundreds of signups for a specific product, that's data your purchasing team needs. The email flow captures revenue, but the signup data informs business decisions beyond marketing.

Measure this flow by conversion rate (signups who purchase after notification), revenue per notification sent, and average time from notification to purchase. Well-optimized back-in-stock flows can see conversion rates of 10-15% — significantly higher than any other automated flow because the intent level is unmatched.

Most Shopify brands treat out-of-stock products as lost sales. With the back-in-stock flow, they become deferred revenue that arrives automatically when inventory returns.