Perpetual Inventory: Definition, Benefits & How It Compares to Periodic
We explain, in simple terms, periodic and perpetual inventory systems, the key formulas, and the pros and cons of each approach for small manufacturers.
Perpetual inventory is an inventory management method where stock levels and valuations are updated continuously in real time — every time you purchase materials, manufacture a product, or make a sale. Unlike periodic inventory (where you count everything once a year), a perpetual system gives you an always-current view of what you have on hand and what it’s worth.
The IRS and GAAP (Generally Accepted Accounting Principles) rules both state that you have the choice to either count your complete inventory on an annual basis once a year or maintain a perpetual (constantly counting) counting system. So, which method of tracking is generally best?
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To find out, we’ll cover everything you need to know about periodic and perpetual inventory management systems, including some examples so you can see how they work in practice.
Periodic inventory systems
Periodic Inventory involves counting and recording your stock levels every once in a while (i.e. on a “periodic” basis). For most small businesses that use this approach, this count only occurs annually to provide financial figures for tax purposes however you can also use this method quarterly or even monthly if your workflow allows. Most periodic systems tend to be very simple inventory spreadsheets or paper journals.
The periodic method involves stopping all production and sales on a specific date and then undertaking a complete count of your inventory in this “frozen moment in time”.
The number on hand is noted, along with a calculated unit price in your periodic inventory system. Your quantity on hand multiplied by your unit price becomes your material inventory valuation for the material.
This method is relatively easy if you have a very small inventory as you only need to set aside a day or so at the end of the year to do your basic count, however can be tricky to calculate materials that are now tied up in your unsold stock and the true “landed cost” of your materials.
Because you are only counting your stock at the end of the year, you won’t have much visibility on your actual stock levels, so you’ll need to be “eyeballing” your stock regularly to determine what materials you are running low on. You’ll also be completely unaware of any unexpected stock loss (i.e. damaged stock) so can do little about this situation when it is found at the end of the year.
Periodic inventory accounting
In terms of your accounting, only information gathered during your physical counts can be used to balance your ledgers. Usually this involves adding the balance to your beginning inventory at the start of the next financial period.
Ending inventory and COGS are also done at the end of the financial period in a periodic system for the same reasons - in between these financial start and end periods, only estimates of material usage, inventory and COGS can be generated and used for reporting and forecasting.
Industries and businesses that suit periodic inventory
Periodic inventory tracking systems usually only suit very small business operations, this is mostly due to the physical and manual requirements involved.
If your business has more than one warehouse or physical location for your stock, periodic inventory is not recommended unless you have a way of tracking stock transfers between locations.
It can however be an excellent starting point to inventory management for very small businesses that are not looking for significant growth, or are not looking to expand their operations outside one physical location. Periodic inventory can also be a good solution if a business isn’t clear about their exact requirements in terms of featureset - once this is defined, then a perpetual system can be found that meets these needs.
Pros of periodic inventory systems
- The periodic system is relatively easy if you have a very small inventory as you only need to set aside an hour or two at the end of the year to do your basic count (but don’t forget to also count any materials tied up in your unsold stock!).
- If the purchase prices of your materials haven’t varied, or if you haven’t restocked very often through the year unit prices can often be fairly simple to calculate by hand.
- As a consequence of this method’s simplicity, it is quite appropriate to use simple systems like paper books or spreadsheets to track and count.
Cons of periodic inventory systems
- As you are not keeping records of inventory levels during the year, you’ll need to constantly be “eye-balling” your stock levels to ensure that you don’t run out of materials you need to produce your products. This in reality means several ad-hoc stocktakes through the year rather than the one, so you’ll need to factor this time in.
- If you have a large inventory, once a year counts can be very time intensive and prone to error - especially if you are a solo entrepreneur trying to get orders out at the same time.
- If you purchase many lots of the same materials at different prices during the year, calculating your unit price can be time consuming and difficult.
- This system puts all the work at the end of the financial year when your figures are due: this is one of the most stressful times in the year for a small business. For self-employed people, having an unexpected event occur around this time (sickness, large influx of orders) could jeopardise your chances of getting these numbers together in time for the deadline and thus you risk the chance of fines.
- Your COGS (Cost of Goods Sold) final figure will not be known until year end, so you’ll need to be ready for an unexpected tax total if your cost of manufacture is less than expected.
- This system doesn’t tend to scale well as you grow your business - eventually you’ll need to switch to something more robust when your inventory and purchasing activities become too complex to track using spreadsheets and paper.
- It can be difficult to keep your records with enough granularity to satisfy IRS auditing - you’ll need to make sure that you “show your working” for any material unit cost calculations you are doing manually and ensure that they are in line with the IRS recommendations (i.e. FIFO, LIFO or Rolling Weighted Average)
Perpetual inventory systems
The word ‘perpetual’ means doing something on a continuous, ongoing basis.
Perpetual inventory means that the counts and calculations are done constantly in real-time rather than at certain times during the year.
Rather than updating a spreadsheet with new counts each year, you update a system with stock changes as they occur: when you make your product, sell it, or purchase new stock. This gives you real-time stock and valuation data so that you can see your exact stock situation at any time.
By using perpetual inventory systems, a business can also adopt a number of automated processes like barcode or QR scanning or even RFID tagging to track goods as they move in and out of the warehouse locations.
Some examples of popular perpetual inventory systems include Craftybase, QuickBooks Manufacturing, and Unleashed. If you’re comparing options, see our roundup of the best inventory management systems for small manufacturers for a detailed breakdown.
A perpetual system does all the calculations that are required to produce the numbers you need. You’ll, however be responsible for entering in the data for your expenses and manufactures as they occur and manually checking for accuracy via regular stocktakes.
A big advantage to using a perpetual inventory management system is seeing stock levels in real-time, as this provides the ability to react to low stock situations quickly…and even predict when they will occur ahead of time.
Stocktaking using the cycle count approach allows you to further assess and refine your usage of materials and make improvements to your processes throughout the year.
Pros: perpetual systems offer businesses greater accuracy when it comes to tracking their inventory levels, meaning they can better predict demand and make more informed decisions about their production lines.
Cons: perpetual systems are more expensive to implement and require a lot of resources to maintain.
Pros of perpetual inventory systems
- More accurate than periodic systems
- Always up-to-date, with real time data available at all times
- Lower risk of stockouts or overstocking due to stock visibility
- Allows for Work in progress (WIP) accounting
- Suitable for inventories of all sizes
- Provides real-time cost of goods sold (COGS)
- Access to more data to guide business decisions
- Less internal time wasted on stocktakes and manual accounting
- Reduced risk of human errors during stocktake
Cons of perpetual inventory systems
- Steeper learning curve to learn accounting principles
- Takes time to properly implement processes around managing stock
- Events must be logged in real-time and correctly to get accurate counts and valuations
- Extra costs for dedicated software
- Occasional stocktakes are still recommended for accuracy checking
Perpetual inventory formula
The core formula behind a perpetual inventory system is straightforward:
Ending Inventory = Beginning Inventory + Purchases − Cost of Goods Sold (COGS)
In a perpetual system, this calculation is updated continuously rather than at the end of an accounting period. Every time you record a purchase, manufacture, or sale, the system recalculates your inventory balance automatically.
For COGS specifically, the formula under perpetual inventory is:
COGS = Beginning Inventory + Purchases − Ending Inventory
The key difference from a periodic system is that these numbers are always current. You don’t have to wait until year-end to know your inventory value or your cost of goods sold — the system tracks it for you in real time using whichever cost flow method you’ve chosen (FIFO, LIFO, or Weighted Average).
Perpetual vs periodic inventory: a side-by-side comparison
| Feature | Periodic Inventory | Perpetual Inventory |
|---|---|---|
| Stock updates | At scheduled intervals (monthly, quarterly, yearly) | Continuously in real time |
| COGS calculation | End of period only | Updated with each transaction |
| Accuracy | Lower — relies on physical counts | Higher — real-time tracking |
| Technology required | Spreadsheets or paper | Dedicated inventory software |
| Cost to implement | Low | Moderate |
| Best for | Very small businesses, simple operations | Growing businesses, multiple products/locations |
| Stocktakes needed | Required for all data | Only for accuracy verification |
| Scalability | Limited | High |
Examples of perpetual and periodic inventory systems
Now that you understand the difference between periodic and perpetual inventory systems, let’s look at an example of how each works for small businesses.
Periodic inventory example: Jim
Jim owns a woodworking business and has a team of 3 staff. Jim is currently using a periodic inventory system, which means he and his staff take a physical inventory count on the 1st of every month.
This involves walking around the workshop, counting each raw material and finished product, and entering the updated count in their Excel inventory spreadsheet.
During the month, Jim doesn’t know his exact stock levels and can only make manufacturing and purchase decisions after the monthly count is complete.
To create a view of total inventory value on hand, Jim can estimate this by multiplying his average unit cost per material or product by the amount in stock. This is an estimate as it does not account for the amount of stock bought at different prices throughout the year.
Perpetual inventory example: Kate
Kate owns an apparel manufacturing company with a team of 5 staff members. Kate uses a perpetual inventory system, which means she and her staff are continuously tracking inventory levels as goods move in and out of their warehouse.
Each time a raw material is purchased, the team updates its online inventory platform with the quantity purchased. The system automatically calculates the new inventory stock level for that material.
When a finished product is shipped, the system is then also updated to reflect the deduction in inventory to show real-time product stock levels.
This means Kate and her staff have visibility of their inventory stock levels at any given time, allowing them to make informed decisions about their product line and purchase orders.
Kate can also calculate a very accurate inventory valuation based on her stock on hand, as her perpetual inventory system tracks each purchase of raw materials / product and its usage / sale.
Which inventory system is right for handmade makers?
If you run a handmade business — soap, candles, jewellery, food products, or any small-batch manufactured goods — perpetual inventory is almost always the better choice. Here’s why.
Makers don’t just sell products. They make them, and that changes everything about how inventory needs to be tracked. When you buy beeswax and fragrance oil to produce 50 candles, a periodic system can tell you how much wax you have on hand at year-end. A perpetual system tells you exactly how much wax you’ve consumed per batch, what each candle costs to make, and what your current materials are worth — right now, not in twelve months.
This matters for three reasons that are specific to makers:
1. Recipe costing is only possible with perpetual tracking. Knowing what a product costs to make requires tracking every material that goes into it. Periodic systems can’t do this because they don’t record transactions — they only record counts. If you’re pricing your products based on guesswork rather than actual material costs, you’re likely leaving money on the table (or losing it altogether).
2. Etsy, Shopify, and multi-channel selling makes manual counts unreliable. If you’re selling across multiple platforms, your inventory is moving constantly. By the time you do your annual count, your figures are already out of date. A perpetual system syncs with your sales channels and adjusts stock automatically.
3. Tax time becomes manageable. Under a periodic system, calculating your COGS for Schedule C means doing a full stocktake at year-end and working backwards. Under a perpetual system using FIFO or weighted average cost, your COGS is calculated automatically throughout the year — and your year-end figures are already waiting for you.
The main drawback is setup time: entering your materials, recipes, and opening stock levels upfront takes effort. But once you’re running, a perpetual system saves you far more time than it costs. Most makers find that the switch pays for itself within the first tax season.
Conclusion
The IRS and GAAP rules both state that you can either count your complete inventory on an annual basis or maintain a perpetual system — both are fully tax-compliant in the US.
For very small businesses with simple operations and minimal stock movement, periodic inventory can still be an appropriate starting point. But for any maker who is tracking recipes, selling on multiple channels, or looking to grow, perpetual inventory is the clear choice. The accuracy, the real-time visibility, and the tax-ready reporting are well worth the investment in proper software.
Craftybase: perpetual inventory software built for makers
Craftybase is designed specifically for small-batch manufacturers — the kind of business where a perpetual system isn’t just helpful, it’s essential.
Where general inventory tools track finished product quantities, Craftybase tracks your raw materials all the way through to finished goods. You enter your recipes (called manufacturing runs), and Craftybase automatically deducts the materials used and calculates your cost per item. Every purchase, every production run, every sale updates your inventory in real time.
Key features for makers:
- Recipe costing — calculate the exact material cost of every product you make, including labour if you choose to track it
- Automatic COGS — your cost of goods sold is calculated continuously, not just at year-end, using FIFO or weighted average cost
- Etsy and Shopify sync — orders import automatically, so your inventory stays accurate without manual data entry
- Low stock alerts — get notified when materials fall below your reorder point, before you run out mid-production
- Tax-ready reports — pull your COGS, inventory valuation, and material usage reports at any time for your accountant or Schedule C
Try Craftybase free for 14 days and see how much clearer your numbers look when everything is tracked in real time.
Frequently Asked Questions
What is perpetual inventory?
Perpetual inventory is an inventory management method where stock levels and valuations are updated in real time with every transaction — purchases, sales, and manufacturing runs. Instead of counting everything once a year, the system keeps a running tally so you always know what you have on hand and what it's worth. This is the standard approach for any business that manufactures products from raw materials.
What is the difference between perpetual and periodic inventory?
The key difference is timing. Periodic inventory updates stock counts at set intervals — usually once a year — using a physical count. Perpetual inventory updates continuously as transactions occur, so your figures are always current. Periodic systems rely entirely on physical counts for accuracy; perpetual systems use physical counts only to verify what the software already knows.
What is the perpetual inventory formula?
The core perpetual inventory formula is: Ending Inventory = Beginning Inventory + Purchases − COGS. In a perpetual system, this equation is recalculated automatically with every transaction rather than at period-end. COGS itself is calculated as Beginning Inventory + Purchases − Ending Inventory. Because everything updates in real time, both figures are always current — you don't need to wait until year-end to know where you stand.
Is perpetual inventory FIFO or LIFO?
Perpetual inventory systems can use any cost flow method — FIFO (First In, First Out), LIFO (Last In, First Out), or Weighted Average Cost. The system applies your chosen method automatically to each transaction as it occurs, rather than calculating it manually at the end of the period. Most small makers use FIFO or weighted average cost, as these tend to reflect actual usage most accurately.
Which inventory system is better for handmade businesses?
Perpetual inventory is almost always the better choice for handmade businesses. Because makers transform raw materials into finished products, you need to track material consumption at the recipe level — not just finished product quantities. A periodic system can't tell you what each product costs to make or alert you when materials are running low. Craftybase is built on a perpetual model specifically because it's the only approach that works for small-batch manufacturing.
When should I switch from periodic to perpetual inventory?
Most makers benefit from switching when they start carrying more than a handful of materials, selling across multiple channels, or finding that year-end stocktakes are stressful and error-prone. The clearest signal is when you're spending more time managing spreadsheets than making products — or when you realise you don't actually know what your products cost to make. The earlier you switch, the easier the transition; waiting until you're at high volume makes the initial data entry much more painful.
