Back-in-Stock Flows: The Easiest Revenue You're Not Collecting

When a product sells out on your Shopify store, what happens? For most brands, the answer is: absolutely nothing. The customer lands on the page, sees "Sold Out," shrugs, and leaves. Maybe they buy from a competitor. Maybe they forget about you entirely.

That's revenue walking out the door. And it's insane — because these are the highest-intent visitors you have. They already know what they want. They already decided to buy. The only reason they didn't is that you didn't have the product in stock.

A properly built back-in-stock flow in Klaviyo captures that demand, holds it, and converts it the second inventory comes back. We run these flows for 150+ brands at GOSH Digital, and across our portfolio, back-in-stock emails average a 65% open rate and a 14% conversion rate.

Let me say that again: 14% conversion rate. That's 5-10x what a normal campaign gets. Because you're emailing people who already want to buy.

If you're not running a back-in-stock flow, you're leaving the easiest revenue in eCommerce on the table.

Why Back-in-Stock Is the Most Underrated Flow in Klaviyo

The typical Klaviyo account has maybe 5-7 active flows: welcome series, abandoned cart, browse abandonment, post-purchase, winback, and maybe a sunset flow.

Almost nobody has a back-in-stock flow.

Here's why it matters so much:

Demand signals are captured. When someone signs up for a back-in-stock alert, they're telling you exactly what they want. That's zero-party data. Use it.

Conversion is almost guaranteed. The intent is already there. You're not convincing someone to buy — you're telling someone their desired product is available again.

Revenue timing is predictable. The moment inventory is restocked, the revenue comes in. It's like turning a faucet on.

It protects your ad spend. If you're running paid ads to a product that sells out, every click after stockout is wasted money. A back-in-stock capture form turns those wasted clicks into future revenue.

Here's a real example: One of our apparel clients had a jacket sell out during a fall campaign. In the 3 weeks it was out of stock, 2,400 people signed up for back-in-stock alerts. When it restocked, we sent the notification — and generated $87,000 in revenue within 48 hours. From a single email.

Setting Up the Back-in-Stock Capture

Step 1: Add a "Notify Me" Button to Sold-Out Products

When a product variant is sold out on Shopify, the default behavior is to either hide the add-to-cart button or show a greyed-out "Sold Out" button. Neither is helpful.

Replace it with a "Notify Me When Available" button that captures their email address.

How to do this in Klaviyo:

1. Go to Klaviyo and navigate to the "Back in Stock" section under Forms
2. Klaviyo has a native back-in-stock feature — enable it
3. Customize the form to match your brand styling
4. Add the snippet Klaviyo provides to your Shopify theme

The native integration tracks which specific product variant the customer signed up for. This is critical — you don't want to notify someone who wanted the blue jacket size medium that the red jacket size XL is back in stock.

Alternative apps: If you want more customization, Klaviyo's native back-in-stock is solid for most brands. For stores with hundreds of SKUs and complex inventory, apps like Back in Stock by Appikon add extra features like waitlist prioritization and demand analytics.

Step 2: Capture More Than Just Email

The default back-in-stock form asks for an email address. That's fine. But you can do better.

Add an SMS opt-in checkbox: "Also notify me by text." Back-in-stock SMS messages have a 98% open rate and convert even faster than email because the urgency is immediate.

Add a note about scarcity: "Join 847 others waiting for this product." Social proof on the capture form increases signups by 15-25%. If 847 other people want this product, it must be good.

Step 3: Build the Email Flow in Klaviyo

Here's the exact flow structure:

Trigger: Klaviyo's back-in-stock trigger (this fires automatically when a tracked product comes back in stock)

Important timing note: Set the flow to check inventory levels every 1-2 hours. You don't want a 24-hour delay between restocking and notification — products can sell out again.

The 3-Email Back-in-Stock Sequence

Email 1: The Instant Notification (Sent Immediately)

Subject line options:

• "It's back! [Product Name] is in stock"
• "Good news, [first name] — [Product Name] just restocked"
• "The wait is over. [Product Name] is available now."

Email content:

Keep this short. Brutally short. The customer already knows the product. They already want it. Your only job is to tell them it's available and get them to the product page.

Hero image: The product photo. Large, clear, impossible to miss.

Body (3 lines max): "Great news — the [Product Name] you've been waiting for is back in stock. Sizes are limited, so we wanted to let you know first."

CTA button: "Get Yours Before It Sells Out" — link directly to the product page, ideally with the correct variant pre-selected.

Scarcity note: "Last time this product sold out in [X days/hours]." If you have this data, use it. Real scarcity data drives urgency without feeling manipulative.

Email 2: The Urgency Follow-Up (24 Hours Later)

Send only to: People who opened Email 1 but didn't purchase.

Subject line: "Still available — but going fast" or "Your [Product Name] won't last long"

Content: "Just a heads up — the [Product Name] you wanted is still in stock, but based on demand, it won't be for long. [X number] people were waiting for this restock."

Add a product recommendation block: "You might also like..." showing 3-4 related products. This captures people who might have been waitlisted for one product but would be happy with an alternative.

Email 3: The Last Chance (48-72 Hours After Restock)

Send only to: People who received Email 1 and Email 2 but didn't purchase.

Subject line: "Last chance — [Product Name] selling out again"

Content: Short message about remaining inventory. If you can pull live inventory counts into Klaviyo, do it: "Only 23 left in stock."

Optional incentive: A small incentive can push fence-sitters over the edge. "Take 10% off your order — just because you waited." Use a unique code with a 48-hour expiration.

This third email converts the hesitators. We typically see 5-8% conversion on Email 3 alone — customers who needed one extra nudge.

Adding SMS to the Flow

If the customer opted into SMS notifications, send an SMS alongside Email 1. The SMS should fire at the same time or even slightly before the email.

SMS message: "Hey [first name]! The [Product Name] you wanted is back in stock. Grab it before it sells out again: [link]"

Keep it under 160 characters. Direct link to the product page. No fluff.

Why SMS first: SMS gets read within 3 minutes on average. Email gets read within 3 hours. For limited-stock restocks, those hours matter. The first people to see the notification get the product. Everyone else gets a second sold-out experience.

Using Back-in-Stock Data for Inventory Decisions

Here's a side benefit nobody talks about: your back-in-stock waitlist is a demand forecasting tool.

If you have 500 people waiting for a product restock, you know exactly how many units to order. If a color variant has 3x the waitlist of other colors, you know where to allocate production budget.

We help clients use back-in-stock data to:

• Set minimum reorder points (product needs 50+ waitlist signups before reordering)
• Prioritize which out-of-stock items to bring back
• Identify which variants (size, color, flavor) have the highest demand
• Calculate expected revenue from a restock before placing the PO

One supplement client used their waitlist data to discontinue 4 low-demand flavors and triple their order on 2 high-demand flavors. Revenue from that product line went up 35% with lower inventory costs.

Advanced: Conditional Splits in the Back-in-Stock Flow

Not all back-in-stock customers deserve the same treatment. Use Klaviyo's conditional splits to personalize the flow:

Split by predicted CLV: High-CLV customers who are waiting for a restock should get the notification first — even 30-60 minutes before everyone else. This is VIP treatment that drives loyalty.

Split by number of signups: Someone who's signed up for back-in-stock alerts on 3+ products is highly engaged with your brand. Give them a small incentive — free shipping or a bonus gift — to convert.

Split by original traffic source: Did they find the sold-out product through a paid ad? Consider a slightly higher discount since they've already "paid" attention once and were disappointed.

Common Back-in-Stock Mistakes

Mistake 1: Slow trigger timing. If your flow checks inventory every 24 hours, products can restock and sell out again before the notification even sends. Set your trigger to check every 1-2 hours.

Mistake 2: Sending to everyone at once. If 5,000 people are on the waitlist and you only restocked 200 units, don't email all 5,000. You'll create a terrible experience for the 4,800 people who click through to another sold-out page. Stagger your sends or cap the notification list based on available inventory.

Mistake 3: Generic subject lines. "Back in Stock" is bland. Include the product name. Make it specific. "Your Lavender CBD Gummies Are Back" hits way harder than "Back in Stock."

Mistake 4: No scarcity messaging. If a product sold out once, it can sell out again. Remind people of that. Real scarcity (not fake scarcity) is your best friend in back-in-stock emails.

Mistake 5: Forgetting mobile. These emails need to look perfect on mobile. One product image, short copy, big CTA button. That's it. Don't overcomplicate the design.

Quick Setup Checklist

Here's your action plan:

1. Enable Klaviyo's back-in-stock feature in your account
2. Add the "Notify Me" button to your Shopify theme on sold-out variants
3. Build the 3-email flow in Klaviyo with the structure above
4. Add SMS notifications for subscribers who opt in
5. Set up conditional splits for VIP and high-engagement customers
6. Test the full flow by setting a product to out-of-stock, signing up, and restocking
7. Monitor the waitlist data monthly for inventory insights

This entire setup takes about 2-3 hours. The revenue it generates is effectively passive — it runs automatically every time a product restocks. Across our client base, back-in-stock flows account for 3-8% of total email revenue with virtually zero ongoing maintenance.

It's the easiest revenue in eCommerce. Stop leaving it on the table.

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Mark Cijo is the founder of GOSH Digital, a Klaviyo Gold Partner agency that's driven over $70M in revenue for 150+ eCommerce brands. If you want us to build out your full Klaviyo automation suite — back-in-stock flows included — book a free strategy call.