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Originally published on November 10, 2021 Last updated on March 6, 2026

Perpetual Inventory System

If your business uses a periodic inventory system where you frequently update your stock levels and conduct physical stock takes, the idea of an inventory system that updates automatically in real time sounds pretty enticing. Indeed, transitioning to a perpetual inventory system has many advantages, including saving you time and providing you with more accurate […]
perpetual inventory system

If your business uses a periodic inventory system where you frequently update your stock levels and conduct physical stock takes, the idea of an inventory system that updates automatically in real time sounds pretty enticing. Indeed, transitioning to a perpetual inventory system has many advantages, including saving you time and providing you with more accurate inventory records. Learn more about perpetual inventory and how you can implement it in your own business.

What Is a Perpetual Inventory System?

A perpetual inventory system is a method for tracking stock quantities using sales and purchasing records. It’s in opposition to a periodic inventory system, which requires manually counting inventory on a regular schedule. A perpetual inventory system requires specialized stock tracking software, which automatically deducts and adds items to your stock quantities based on your sales and purchases. Businesses that sell goods in physical retail stores also require a point of sale (POS) system, integrated with the inventory software, to decrement sales in real time.

For the most part, a perpetual inventory system requires no manual data entry. The stock quantities automatically rise and fall thanks to integrations with your sales channels and a purchasing and order management system included with the inventory software. The only manual adjustments required occur when the automated count falls out of line with physical counts, which occurs when an item breaks or gets lost or stolen. A physical count once a year is usually sufficient to correct these records.

A perpetual inventory system also has some unique accounting applications. Under the perpetual inventory tracking system, businesses can keep a running total of the cost of goods sold and the cost of goods available for sale. Therefore, the accounting team doesn’t have to maintain a separate purchases account because purchases are directly attributed through the inventory account.

How to Use a Perpetual Inventory System

A perpetual inventory system starts with a system for automatically logging sales and purchases. For many businesses, that means using barcode scanners to track inventory and the point of sale. In Finale Inventory, you can log purchases automatically by creating your purchase orders directly in the software. If you use reorder point settings, purchase orders will automatically generate the quantities you need, using costs from your supplier catalogs. All you have to do is hit send.

Once you have a system that tracks your inventory in real time, you can apply a perpetual inventory accounting system. To do so, you must understand the accounting concept of “cost of goods sold,” or COGS. Essentially, COGS is all the direct costs incurred to acquire and manage merchandise before it’s sold. It includes purchasing costs, labor and materials but not distribution or sales costs. The COGS formula is beginning inventory plus inventory purchases, minus ending inventory. 

In Finale Inventory, we handle this using the average costing method. The key here is that every average COGS is calculated at the time of transaction since this system is perpetual. For example, before you make a sale, you purchase units at two different price points. When the sale occurs, the COGS recorded is an average of the purchasing prices at that time. 

If you later purchase more units at a third price point, that’s not factored into the COGS for previous purchases. However, the COGS will be recalculated on your next sale to include the most recent purchasing cost. If you use Finale Inventory, your average COGS updates automatically based on your purchasing records.

Using Perpetual Inventory Accounting

Once you understand your average COGS, you can create the appropriate accounting entries for every inventory transaction. Some events that require an accounting entry include:

  • Purchasing inventory: Debit your inventory account and credit your accounts payable.
  • Incurring inventory-related expenses, such as shipping: Debit your inventory account and credit your cash or accounts payable.
  • Returning goods to a supplier: Debit the accounts payable and credit the inventory account.
  • Selling inventory: First, debit your accounts receivable and credit your sales. Then, debit your COGS and credit your inventory account.
  • Accepting customer returns: First, debit your sales account and credit your accounts receivable. Then, debit your inventory and credit your COGS.
  • Adjusting inventory after a physical count: Mark your inventory over and short account with a debit and credit your inventory account.

How a Perpetual Inventory System Works

The perpetual inventory system follows four steps. With powerful real-time stock management software leading the process, very little has to be performed manually. The steps in a perpetual inventory management system include:

  1. Point of sale: If you have a brick-and-mortar store, you’ll log sales using a POS system compatible with your inventory management software, such as Lightspeed or Square POS. If you sell online, you’ll integrate your inventory software with your e-commerce channels, such as Amazon or your online shopping cart platform. When a sale happens on any platform, the inventory records the selling price update in your central database.
  2. COGS recalculations: When a sale is recorded, the COGS updates according to the costing averages of recent stock purchases listed in the inventory software.
  3. Automated reorder point calculations: Another benefit of perpetual inventory tracking is keeping items stocked at optimal levels. Your inventory software uses a dynamic reorder point formula that accounts for your current sales trends, current inventory levels, desired buffer stock and supplier lead times. It’ll calculate precisely when and how much to reorder and generate a purchase order for you to sign and send. Confirmed purchase orders provide the latest pricing information to update the average COGS on future sales.
  4. Replenished inventory: When new stock arrives in your warehouse, your employees use a barcode scanner to add the new inventory to your system. This step updates your inventory levels in your central database alongside your POS and online sales channels.

What Are the Advantages?

The beauty of a perpetual inventory system is more accurate inventory records with less manual work, so your inventory managers can enjoy more infrequent stock counts. If you use inventory management software that integrates with your accounting software, your accounting team can watch your COGS and inventory transactions update in real time.

Some of the benefits of this system include:

  • Real-time data: Real-time data helps your team make better decisions and prevents many inventory issues, such as overselling. With real-time inventory records, your available quantities push to your online marketplaces every five minutes. It prevents you from selling stock you don’t have and ensures the stock you have available is listed online.
  • Decreased costs and increased sales opportunities: Tracking inventory perpetually means you’re less likely to overstock or understock. You can also safely keep less buffer stock, knowing that a reorder point calculation will help you reorder before your current inventory depletes. This capability saves on holding costs and prevents you from losing sales opportunities.
  • Accurate accounting records: Using information from your sales and purchasing records, your inventory management software can perform many inventory-based accounting procedures and push the data automatically to QuickBooks Desktop or QuickBooks Online. It saves your accounting team considerable time and provides you with many valuable financial reports and documents.
  • Demand forecasting: Using inventory software that can automatically forecast your inventory needs based on your sales velocity is crucial for helping your business grow. You’re less likely to hold excess inventory or run out of stock as your demand increases.

Perpetual Inventory vs. Periodic Inventory

You may be more familiar with periodic inventory since it’s more common for small businesses and those just starting out. This system requires more frequent physical stock counts to measure inventory and the COGS. Usually, companies handle periodic inventory using spreadsheets and perform manual calculations.

Some key differences between periodic inventory and perpetual inventory include:

  • Business stage of development: While a business at any stage can benefit from perpetual inventory management, only new and very small businesses can work effectively with a periodic inventory system. Once a business starts growing and working with higher sales volumes, perpetual inventory is necessary to track merchandise effectively. In fact, it’s a critical investment that can stimulate business growth by cutting inventory holding costs, improving stock availability and reducing shipping times.
  • Software and hardware usage: Perpetual inventory management requires several types of software, including POS software with the related hardware and the inventory management solution — possibly with integrated barcode scanner hardware. While a periodic inventory system requires no special software, it still benefits from accounting software and digital spreadsheets.
  • Frequency of physical counts: Periodic inventory management relies on physical stock counts. Depending on the industry and the way merchandise moves, physical counts could happen each year, quarter or week. Physical counts are much less frequent in a perpetual inventory system and may be performed as infrequently as once a year.

Schedule a Finale Inventory Demo

Finale Inventory is a flexible, scalable inventory management solution that makes a perpetual inventory system possible. We help businesses scale by cutting out manual processes and giving business owners access to real-time data, in-depth insights and easily accessible financial reporting. Schedule a Finale Inventory demo to discover how our inventory management system can change the way you do business.

“The core of maturity, that I see, is starting with a unified view of inventory. I’ve got to be able to accurately represent what do I have, make sure that I know where it’s located so I can get it to my customers quickly.”

— Troy Graham, Descartes

What is the first thing I should fix if I want to scale operations?

Start with a unified view of inventory. The core of maturity starts with being able to accurately represent what you do have and make sure that you know where it’s located to get it to customers quickly. Without a unified view across your warehouses, 3PLs, and vendors, you cannot make the best decisions because you don’t have the best information at hand.

With Inventory Visibility, Businesses Can Make Smarter Allocation Decisions

Once inventory is centralized, businesses can move from reactive updates to intentional allocation. They can decide how much inventory to expose to each channel, when to use buffers, which marketplaces need extra protection, and how seasonality or campaign performance influence availability.

Once I know what inventory I have, how should I decide where to make it available?

Inventory allocation should reflect where orders are coming from, where marketing is working, and which channels carry the most risk. Once you know what you have and where it is located, you can think more strategically using centralized inventory to make prioritization happen automatically. One fertilizer company lost a little over 5,000 orders in one weekend because someone manually uploaded the wrong available inventory to Amazon.

Better Inventory Data Improves Planning, Purchasing, and Growth Bets

Better visibility turns inventory data into a planning tool. With insight into sales velocity, inventory levels, vendors, and channel performance, businesses can make more informed replenishment decisions, avoid overbuying, and test new product lines or vendor-supplied inventory without taking on unnecessary risk.

“You have to have unified inventory to know how to price your products just at that basic level. I can’t price my products if I don’t know the true cost to get it.”

— Mike Bernico, Flxpoint

How does better inventory data help me make smarter buying decisions?

It lets you measure whether your plan is working before you commit more capital. A key question becomes: “Did my plan work? Am I overleveraged in one place or another?” Centralized systems can also help businesses test new product lines or vendor relationships by looking at sales velocity by channel, allowing them to take risks in a calculated and measured way.

Intelligent Order Routing Turns Inventory Complexity Into Automation

Once inventory and supplier data are reliable, businesses can automate fulfillment decisions. Orders can be routed based on cost, speed, margin, location, warehouse priority, vendor fallback, split-shipment rules, or customer expectations. This helps hybrid fulfillment scale because every order does not need a manual review.

How do I decide the best way to fulfill each order?

There is no single answer, which is why order routing needs to account for the context of each order. Intelligent order routing is not just sending an order to someone who has stock; it is taking each and every order and treating it like its own unique use case. Depending on the order, the business may prioritize speed, margin, an internal warehouse, vendor fallback, or preventing split shipments.

Supplier Inventory Sync Extends Inventory Beyond the Four Walls

For hybrid fulfillment to work, supplier inventory needs to become part of the operating model. Supplier sync does not always require advanced technology; it can happen through automated files, FTP, email, APIs, EDI, or ecommerce storefront integrations. The key is replacing manual updates with automated, reliable supplier data.

Can supplier inventory really be treated like part of my own inventory?

Yes, but the goal is not necessarily to force every supplier into a complex integration. Real-time supplier sync can be defined as any way to get an automated update from a supplier, such as Google Sheets, email, FTP, API, EDI, or ecommerce storefront connections. The key is that accurate supplier stock is foundational. If you don’t have an accurate view of what is in stock with your suppliers, you cannot tell your sales channel accurately what’s available.

Exception-Based Workflows Keep Humans Focused Where They Matter

Automation does not remove people from the process. Mature operations let technology handle the routine majority while humans focus on exceptions, such as high-value orders, fraud risk, compliance requirements, restricted products, export rules, or unusual fulfillment scenarios.

If my business has special cases, can automation still work?

Yes. The point is not to automate every possible decision; it is to automate the routine work and surface the exceptions. Businesses should not have to look at every single order. Instead, technology can highlight high-value orders, risky locations, or compliance requirements. The goal is to take care of the 80% of workflows that are obvious while still allowing human review when specific exceptions arise.

The Right Inventory Technology Should Fit the Business, Not Overwhelm It

Software decisions should be based on business fit, not popularity, feature volume, or broad “all-in-one” promises. Growing ecommerce businesses should identify their highest-impact bottleneck, prioritize what matters now, and choose technology that is right-sized but flexible enough to support future phases of growth.

How should I choose software without overbuying or picking the wrong system?

Start with your priorities, not the biggest feature list. Avoid an all-in-one system that claims to “do everything under the sun” and look for a “best of breed approach” with systems that can scale as you add channels or vendors. The practical advice is to stack rank what matters now, make sure the system can support future phases, and choose technology that fits your business rather than overwhelming it.

How to Scale Ecommerce Operations Beyond Spreadsheets

For many growing ecommerce businesses, Finale and Flxpoint work together as a practical answer to these challenges. Finale helps centralize and manage internal inventory, purchasing, warehouse operations, and stock visibility, while Flxpoint helps connect vendor inventory, automate supplier sync, and route orders across hybrid fulfillment networks. Together, they give businesses a best-of-breed way to improve inventory accuracy, reduce spreadsheet work, and scale fulfillment without forcing every process into a one-size-fits-all system.

Ecommerce Fulfillment Operations FAQ

What Is Ecommerce Fulfillment Operations?

Ecommerce fulfillment operations are the processes that move an online order from purchase to delivery. This includes managing inventory, syncing product availability across channels, routing orders to the right warehouse, 3PL, supplier, or vendor, and making sure the customer receives the right product on time. As discussed in the webinar, fulfillment is no longer limited to “what’s in my warehouse these days”; growing businesses may rely on internal warehouses, 3PLs, marketplace fulfillment services, and supplier inventory at the same time.

What Are Ecommerce Fulfillment Operation Examples?

Examples of ecommerce fulfillment operations include updating inventory across Shopify, Amazon, Walmart, and other sales channels; allocating inventory to specific marketplaces; sending orders to an internal warehouse, 3PL, or vendor; syncing supplier inventory through files, APIs, EDI, email, or FTP; replenishing warehouse stock based on sales velocity; and flagging exceptions such as high-value orders, compliance requirements, or restricted products. In the webinar, the speakers also discussed hybrid fulfillment examples where a business may fulfill some products from its own warehouse and use vendors as a fallback or extension of available inventory.

How Can I Track My Inventory at an Ecommerce Fulfillment Center?

The best way to track inventory at an ecommerce fulfillment center is to create a unified inventory view that shows what is available, where it is located, and how that inventory connects to each sales channel. That means tracking inventory across internal warehouses, fulfillment centers, 3PLs, marketplace fulfillment programs, and supplier locations instead of relying on disconnected spreadsheets. The webinar emphasized that businesses need to “accurately represent” what they have and know where it is located so they can get products to customers quickly.

How Can I Connect My Inventory to My Supplier?

You can connect supplier inventory through several methods, depending on what the supplier supports. The webinar discussed low-tech and advanced options, including automated Excel or CSV files, Google Sheets, email updates, FTP servers, APIs, EDI, and direct connections to ecommerce storefronts such as Shopify, BigCommerce, or Magento. The key is to ask suppliers how they share inventory today, then use a system that can automate that data flow instead of manually copying supplier inventory into spreadsheets.

What Is Ecommerce Order Routing?

Ecommerce order routing is the process of deciding where an order is fulfilled from after a customer buys. In a simple operation, every order may go to one warehouse. In a more complex or hybrid fulfillment model, the best fulfillment source may depend on inventory availability, shipping speed, cost, margin, customer location, warehouse priority, vendor fallback rules, or whether the order should be split. The webinar described intelligent order routing as treating each order like its own use case, so businesses can automate the best fulfillment decision without manually reviewing every order.

Ready to Take Control of Your Inventory?

Improve inventory, warehouse, and ecommerce operations today.

Request a Demo

Ready to Take Control of Your Inventory?

Improve inventory, warehouse, and ecommerce operations today.

Request a Demo

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