Backlog inventory, or the pileup of sold but unshipped units, is one of the fastest ways to turn strong demand into frustrated customers and shrinking margins. Without a plan, it quietly snowballs. Orders age, support tickets increase, packaging gets rushed, and refunds start creeping in.
Efficient inventory management balances incoming order volume with pick and pack capacity, ensuring inventory that’s already committed leaves the building on time. It also means preventing a backlog caused by inventory that’s available but stuck in transit.
This guide shares an inventory system to help teams clear the queue quickly and keep it from coming back, with steps for improving accuracy, setting reorder points, and optimizing routing.
Backlog inventory is stock that is promised to a customer but still sitting on your shelf. These units have already been sold, yet have not been handed off to a carrier. It’s a work-in-progress queue that fluctuates with your warehouse’s throughput.
A backlog grows when your team ships slower than orders arrive and shrinks when shipping outpaces new demand. Here is the math behind it:
Why does a backlog exist even when you have inventory? Well, retail operations are getting more complex. Some 78% of brands sell on two or more sales channels as of 2025.
Omnichannel volume increases queue pressure and creates edge cases in inventory allocation. For example, you may have global availability, but if the location assigned to the order is empty, the order stalls in the queue. Units might also be physically on-hand, but stuck in receiving, set aside for quality control, or reserved for draft orders.
It’s easy to confuse these concepts, but they point to different problems with distinct fixes.
Don’t know which problem you’re facing? Use this checklist to figure it out:
It’s important to prioritize the right fix. Customers will forgive a backlog delay if you communicate clearly and shipping costs are low (or free). However, they are less forgiving of back orders that come as a surprise.
Inventory backlog happens when orders arrive faster than your team can ship them. It’s not always a bad thing, as it’s often a side effect of growth or high demand, like a Black Friday and Cyber Monday (BFCM) sales peak.
However, if your queue of unfilled orders keeps growing after the rush ends, you’ve got a bottleneck in the supply chain management system that needs fixing. The most common causes of backlog inventory fall into four categories:
To fix your backlog and meet customer expectations, you’ll need better data. Shopify helps solve this by tracking inventory states, separating what is committed to existing orders from what is available to sell. Using smart order routing, you can assign shipments to the right facilities and automate your back order policies to ensure faster delivery times.
A backlog isn’t always a red flag—queues are normal. The real danger is in order aging. Once a backlog starts slipping past promised handling windows, teams get pulled in a spiral.
They receive more “Where is my order?” messages, more manual fixes, more rushed packing, all things that drain time and make the backlog worse. That’s when backlog becomes an operational risk, leading to:
There are a few key steps you can take to fix backlog inventory and prevent it from happening again.
Fixing a backlog starts with knowing what inventory you have. Backlogs can masquerade as a demand problem — but it’s often a data problem. The system believes stock is in the wrong place or does not exist at all, leading to orders that cannot be physically filled.
Start with a seven-day accuracy sprint focused on the top 20 SKUs causing the most unfulfilled orders. In your Shopify admin, verify that products aren’t assigned to extra locations accidentally.
If you use Shopify POS, enforce a barcode scanning rule for all receiving and transfers. Industry data suggests that moving from manual counting to item-level scanning can boost accuracy from roughly 70% to 99%.
Accuracy checklist:
Backlog also builds when replenishment happens too late. The most effective fix is setting clear reorder points (ROP) and safety stock levels so you purchase inventory before you run out.
Use Stocky to access the low stock report. It will automatically calculate a recommended ROP based on your lead times and sales velocity. For a manual check, use the formula ROP = (daily sales × lead time) + safety stock. If you sell five units a day and restocking takes 10 days, reorder when you hit 50 units remaining.
Here are some tips for setting ROPs:
Now that your inventory is accurate and replenished, it’s time to focus on throughput. Backlog comes down to a capacity equation: orders coming in versus orders shipping out.
If you generate 500 orders a day but can only pack 400, your backlog grows by 100 orders daily, no matter how much stock you have. Clear your backlog within the next week with these quick tips:
If your team cannot scale to meet customer demand, it’s a sign to consider outsourcing to a 3PL partner via the Shopify Fulfillment Network.
Compare trusted partners for pricing estimates and performance metrics, then connect your choice to your store admin. You can monitor shipments, inventory levels, returns, deliveries, and more right on Shopify.
If you manage inventory across multiple warehouses or retail stores, back orders can occur when the system sends orders to the wrong location. An order might sit unfulfilled in a warehouse that is out of stock, while the same item is collecting dust on a store shelf.
Use Shopify’s smart order routing to direct orders to the location best equipped to fill them. This prevents an artificial backlog, where you have stock but the order can’t find it.
Set your rules to prioritize efficiency:
Backlogs can build up because teams rely on humans to spot patterns like fast-selling SKUs or stuck transfers. But while humans get tired, automated systems don’t. Use Shopify Flow to build a warning system to catch these issues before they escalate.
The idea isn’t to automate the fixing, but to automate the noticing. When you set up workflows that trigger based on inventory changes or order age, there is less need for manual reporting.
Some examples of no-code workflows to run in Shopify Flow are:
Not all backlog is bad. When it’s intentional, like with preorders or back orders, it can be a strategic choice to preserve revenue. But when you allow back orders on items with unknown lead times, customers will become frustrated and that hurts your brand reputation.
“In this day and age in the consumer psyche, you are battling against Amazon and how they’ve shifted consumers to think you should have a product at your door in two days,” says Marcus Milione, founder of Minted New York.
“But the consumer, when they purchase a product on my website, regardless of how small I am, they think a product should be delivered, you know, within seven days, generally in two days.”
Marcus says that for preorders, added delays in production runs can risk damaging your relationship with your customers.
In Shopify, the setting “continue selling when out of stock” controls this. Enable this only for SKUs with a confirmed inbound purchase order and a stable supplier.
Customers are generally fine waiting if they know they are waiting. They are not fine buying an item they think is in stock, only to receive a delayed email three days later.
No, they are different concepts. Inventory backlog refers to the total queue of unfulfilled orders, and back orders are a policy that lets customers buy out-of-stock items. Back orders can contribute to a backlog, but you can also have a backlog with inventory on hand if you can’t keep up with the volume of orders. A robust inventory management system helps clear an excessive inventory backlog and increase customer satisfaction.
Calculate the volume of backlog items by summing the unfulfilled units on all open order lines, or multiply those units by their selling price to see the revenue value. Calculate backlog days by dividing your total unfulfilled orders units by your average daily shipping capacity.
Normal depends on your business model. Ideally, your backlog shouldn’t exceed your shipping promises. For example, if you promise two-day shipping, the package can’t arrive in five, unless there are supply chain disruptions out of your control. A sign of a healthy backlog is being able to clear it within a standard cycle. If it compounds week over week, you have a bigger problem on your hands.
Increase throughput by adding labor hours, batching picks, and simplifying packaging to ship more units per day. Stop accumulating new backlog by pausing ads on uncertain items and disabling any “continue selling when out of stock” settings where lead times are unreliable. Reducing substantial inventory backlog, however, comes from creating a good plan and optimizing your order fulfillment process long before seasonal events like BFCM.
