Product waitlist: how to measure demand for items that are out of stock

A product waitlist is simply a list of customers who want to buy something that’s currently out of stock. How many sign-ups are there, and how fast are new ones coming in? That’s the cheapest way to measure demand that doesn’t show up in sales. When an item is out of stock, your reports show zero. A flat zero. If you plan only from order history, it’s easy to order too little. Below I explain how to collect sign-ups, which metrics to track and how to turn them into a real order with your supplier.

Why don’t sales show demand for unavailable products?

No stock means zero sales, however many customers wanted to buy. So a sales report measures supply, not demand (a distinction that gets missed surprisingly often in planning). A customer with no way to sign up goes to a competitor, and you never see them again, not even in your data. Product page views? They show interest, but not intent to buy. A much stronger signal is a sign-up for a back in stock notification. After all, the customer leaves their email address for a specific product or variant, and that really means something.

How to collect notification sign-ups so the data is useful for analysis

Put the sign-up form on the page of every out-of-stock product, and make it link each customer to a specific product or variant. Always keep sizes and colours separate. Why? Because demand is usually for one version, not the whole model. Black in M may sell out instantly while beige in XL sits on the shelf. Every record needs a sign-up date, otherwise you can count the total but not the pace. Form copy: say briefly what the customer will get and when. No filler. Oh, and one more thing: a sign-up is consent to be contacted about one specific matter, so it’s a good idea to describe it in your privacy policy.

Which waitlist metrics should you track?

In practice, four numbers are enough: the number of sign-ups, how fast they grow, the share of subscribers who bought once the item was back, and the time from notification to purchase.

• Number of sign-ups - how many people are waiting for a given product or variant; every comparison starts here.
• Sign-up pace - growth per week; if the curve goes up, demand is growing, if it’s flat, interest is fading.
• Notification conversion - the share of subscribers who bought; this is the rate you use to turn sign-ups into actual units.
• Time to purchase - how many days pass between the email and the order; it tells you how quickly a delivery will sell.

In my view, it’s better to compare sign-ups across products and variants than to look at raw numbers alone. Is a hundred sign-ups a lot or a little? It depends on what it sits next to. And don’t take conversion rates from other people’s benchmarks. Calculate them from your own store’s data, otherwise it’s just guesswork.

Planning stock from your waitlist, step by step

The formula is simple: number of sign-ups times your own conversion rate from previous restocks, plus regular sales during the delivery period.

1. Export sign-ups separately for each product and variant.
2. Calculate conversion from the history of earlier notifications.
3. Estimate regular sales for the period when the item will be in stock.
4. Factor in your supplier’s lead time, because the list keeps growing while you wait for delivery.
5. Set the order quantity and priority.

Pace decides the order. Variants whose list grows fastest come first. And what if you don’t have any conversion history yet? Everyone starts somewhere. Place a cautious first order, and after the notifications go out, measure how many people actually bought.

When is a waitlist misleading?

The number of sign-ups can overstate demand. This happens when an item is out of stock for a long time, when a promotion is circulating online, or when one person signs up for several variants at once. Sign-ups also go stale: the longer the gap, the fewer people buy after the notification. Filter out duplicates and test sign-ups before you analyse anything, or you’ll only fool yourself. Then there’s seasonality. Sign-ups collected in winter don’t automatically carry over to summer. In general, treat the list as a signal that you compare with product page traffic and sales history. Not as the only source of truth.

How to run a waitlist in WooCommerce with Klaviyo

In WooCommerce you can collect sign-ups with a plugin that adds a form to the out-of-stock product page and passes customers to a subscriber list in Klaviyo. That’s how the back in stock plugin from K4.pl works: it adds the form, subscribes the customer to the list and emails them when the product is back. You can change the form copy in the settings. For planning, the Klaviyo lists simply become the place where you read sign-ups before placing an order. What about PrestaShop? The measurement method is the same, as long as sign-ups land in one place along with their date.

A well-run product waitlist turns missing stock into purchasing data. Instead of a zero in your report, you get real information. Two things are enough to start: collect sign-ups separately for each variant, with a date, and calculate conversion after every restock. After a few deliveries you’ll have your own rate. And no more guessing when you order.

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