You’ll run out of things. What decides the cost is what happens on the sold-out page and in the inbox of the customer who was about to reorder. Three flows handle most of it: back in stock, substitution, and the late-order notice.

Capture the intent

Every sold-out product page needs a way to say “tell me when it’s back,” by email and, with their consent, by text. Then:

• Give a date or a range. “Back around March 10” beats “coming soon.” If it slips, say so before it passes.
• Reach existing buyers first. If the restock is smaller than the waitlist, send in waves: past buyers, then subscribers, then everyone else. A regular who finds it sold out again has been let down twice.
• Reach out before they ask. Customers due to reorder, from your replenishment timing in The Second Order, should hear about a stockout from you with the date and an alternative, not from the product page.

Explain, don’t discount

The catalog study in chapter 2 also tested what to tell customers whose item was out of stock. Each customer heard one of five scripts: a plain “out of stock,” an explanation that the supplier had a problem, “This item is out of stock because it is extremely popular,” $5 off shipping, or 10% off, the last two offered in return for waiting instead of canceling. The “extremely popular” script and the 10% discount kept about the same share of items (68% and 66%). But the popular script earned $20.51 of profit per out-of-stock item and the 10% discount $15.97, and the two discounts were the least profitable of the five Published.

The long-run result is the one to remember. In the two discount conditions, customers who had met stockouts went on to buy much less than customers who hadn’t: the no-stockout group ordered 24% more units in the following months in the $5 condition, and more than 50% more in the 10% condition Published. One reading is that a discount signals something went wrong that you’re paying to smooth over. Either way, the data gives no support for paying people to wait.

A short, honest reason to wait did as much as a discount, at a lower cost, without the damage later.

So the back-in-stock and delay messages in Appendix B explain and give a date. They don’t apologize with a coupon. If you want to recognize the inconvenience, do it for the customers who waited, after it ships, and not as a price.

Offer something close

Because customers rarely substitute on their own, make the alternative concrete: one or two products, named on the sold-out page and in the stockout email, chosen from what past buyers of the missing product also bought. A different size of the same thing, a sister scent, or a bundle containing it converts better than “you may also like.”

Dell ran a version of this at scale. In Stanford’s case on the company, a phone rep whose customer asked for a configuration could suggest a better component for a small extra payment, which arrived faster “because the component is already in stock” Published. The rep steered demand toward what was on hand, and the customer got something at least as good. That’s the model: the alternative should be equal or better, and it should be the customer’s choice.

Subscriptions and late orders: the rules

Two rules from the FTC’s Mail, Internet, or Telephone Order Merchandise Rule matter here Published:

• Shipping time. You need a reasonable basis to ship within the time you state, or within 30 days if you don’t state one. If you can’t, you must ask the customer to consent to the delay, with a revised date and a free way to cancel, or refund them promptly without being asked.
• Substitutes. You can’t send “materially different” merchandise unless the customer “expressly agrees to the substitution beforehand.” For a subscription, that means a missing product is skipped or delayed with notice, or swapped only with the subscriber’s yes, or under a swap preference they set in advance.

The FTC’s business guide to the rule dates from 2011, with a January 2025 update to penalty amounts. States and other countries add their own requirements; have counsel review your backorder, preorder and subscription-swap language. This isn’t legal advice.

Do this

• Open your top sold-out product on a phone. It should have a back-in-stock signup, an expected date, and one or two named alternatives. Then check what your subscription platform does when a scheduled product is out: if it swaps without asking, change the setting today.