Selling something you don't have yet is easy in Shopify. You tick one box and the product stays buyable at zero.
Everything after that tick is where it goes wrong. Orders slip through to the warehouse, customers don't know when to expect anything, and nobody can say how many people are waiting.
This is the pre-order and backorder system I'd build. Shopify settings and Flow do the sorting. People own the dates and the conversations.
Table of contents
The problem: one checkbox, no system
Shopify's setting is called Continue selling when out of stock. Its help page lists products available for pre-order as one reason to use it.
What the setting does is let customers keep buying at zero or below. It doesn't tell the warehouse to wait, it doesn't give the customer a date, and it doesn't keep a list of who is waiting.
In the US there is also a rule to respect. The FTC's Mail, Internet, or Telephone Order Merchandise Rule says you need a reasonable basis for any shipping time you state, and 30 days if you state none. If you can't ship on time, you have to offer the customer the choice to accept the delay or cancel for a refund.
So a backorder isn't just a stock question. It is a promise with a date on it.
How the system is put together
Six parts: the product setting, tagging the order, holding it, telling the customer, releasing it when stock lands, and who owns what.
Part 1: choose which variants can go below zero
Continue selling is set per product or variant, and only works when inventory is tracked. I'd turn it on only for variants with a confirmed restock or a real launch date, never as a default.
The product page should say it is a pre-order or backorder and give the expected ship date. That date should come from the purchase order, which is why the purchase order reports and days-of-cover alerts matter here.
Part 2: Flow tags the order
A Shopify Flow workflow starts on Order created. A condition checks whether any line item is on a variant that has gone to zero or below, or carries a pre-order tag on the product.
If it matches, the Add order tags action tags it "backorder". I'd build and test the condition on real orders, because it is the part most likely to be wrong.
Part 3: Flow holds the fulfillment
The same workflow runs Hold fulfillment order. Shopify's help page says it sets the order to On hold, and held orders aren't fulfilled until the hold is removed. It has a reason, optional notes and a notify-merchant option.
Shopify's holds page says inventory stays reserved while fulfillment is blocked. It also says the Flow hold template needs your fulfillment service added to its criteria, so check how your 3PL treats held orders before relying on it.
One decision to make up front: an order-level trigger holds every fulfillment order on that order. If a customer buys one in-stock item and one backorder, the whole order waits unless you choose to split it.
Part 4: tell the customer, with a date
Flow's Send internal email action alerts support when a backorder comes in. Support sends the customer a template with the expected date and how to cancel.
If the date slips, support sends a new notice before the old date passes. Under the FTC rule, that notice needs a new date or an explanation, and a way to cancel at your expense.
Part 5: release oldest first
Flow has a Product variant back in stock trigger. I'd use it to email the operations owner, not to release orders automatically at first.
The owner filters orders by the backorder tag, releases holds oldest first until the new stock runs out, and removes the tag. Flow's Release fulfillment order holds action can automate this later, once the manual version runs cleanly.
Part 6: what is automatic and what a person does
Automatic: tagging backorders, holding them, and alerting support and operations.
A person: deciding which variants can go below zero, setting the ship date, sending delay notices, releasing holds, and handling cancellations.
Ownership: the buyer owns the restock date. Support owns customer notices. The operations manager owns the workflow and the release. Each backorder batch gets a row in the exceptions tracker, and the count goes into the Friday founder update.
What it solves
Shipping what isn't there. Held orders don't go to the pick list.
"Where is my order?" Customers get a date before they have to ask.
Missed promises. New dates go out before old ones pass, not after.
Unfair release order. The oldest orders ship first when stock lands.
No visibility. Anyone can count tagged orders and see how many people are waiting on each product.
The effect on the business, and how to measure it
I'm not quoting results here. I don't have published numbers for this build, and I won't invent them.
The target is simple: no backorder shipped by mistake, and no backorder customer who hasn't been told a date. That is a target, not a result.
Here is what I'd baseline before building, and compare after.
Backorders open. Tagged orders still on hold, by product.
Days waiting. From order to shipment for tagged orders.
Date accuracy. Promised ship date versus actual ship date.
Cancellations and refunds. How many backorder customers cancel, and after how long.
Contacts per backorder. Support tickets asking for an update on tagged orders.
Slips. Backorder items that reached the warehouse or 3PL by mistake. This should be zero.
Where it shows up in the business: cash from sales you'd otherwise lose at zero stock, fewer support contacts, fewer chargebacks from customers who gave up waiting, and clean records if a customer disputes a delay.
The bigger picture: selling ahead of stock is a promise
Pre-orders and backorders let a brand keep selling through a stock gap. That only works if the promise is managed as carefully as the stock.
This system sits between the systems I've written about before. Days-of-cover alerts warn you before you hit zero. Order routing keeps problem orders away from the warehouse. The returns system handles refunds when a customer cancels.
And in peak season, when restock dates move, the delay notice is what keeps a backorder from turning into a complaint.
Build checklist
- List every variant currently set to continue selling when out of stock, and turn it off where there is no confirmed restock.
- Agree who owns the restock date for each pre-order or backorder product.
- Add clear pre-order or backorder wording and the expected ship date to the product page.
- Build the Flow workflow: Order created, a condition for backordered items, Add order tags, Hold fulfillment order.
- Test it on real orders, including a mixed order with one in-stock item.
- Check with your 3PL how held orders are treated before going live.
- Write the first delay notice and the renewed notice, both with a cancel option, for support to use.
- Add a back-in-stock alert to the operations owner and a written release routine, oldest first.
- Log each backorder batch in the exceptions tracker and report the open count weekly.
- Baseline days waiting, date accuracy, cancellations and contacts per backorder, and review monthly.
The checkbox makes the sale. The system makes sure the customer gets what they were promised, or hears about it in time to decide.
Source: tool details checked against Shopify Help Center pages on selling when out of stock, holding fulfillments, the Flow Hold fulfillment order action, Flow actions and Flow triggers. Delay and cancellation rules from the FTC's Business Guide to the Mail, Internet, or Telephone Order Merchandise Rule (US only, not legal advice). The system design and the expected effects are my own operator view.
Frequently asked questions
Does "Continue selling when out of stock" handle pre-orders on its own?
No. It lets customers keep buying at zero or below. It doesn't hold fulfillment, give a ship date or track who is waiting, so you need tagging, holds and customer notices around it.
Can Shopify Flow stop backorders from shipping?
Flow's Hold fulfillment order action sets an order to On hold, and held orders aren't fulfilled until the hold is released. Check with your 3PL how they treat held orders.
What do I owe a US customer if a backorder is late?
The FTC's guide says you must offer a choice to accept the delay or cancel for a prompt refund, with a new date or an explanation. A second delay needs the customer's active agreement.
What should I measure?
Backorders open, days waiting, promised versus actual ship date, cancellations, support contacts per backorder, and any backorder that reached the warehouse by mistake.