Inventory Accounting: Methods, COGS, &...

Inventory Accounting: Methods, COGS, & Bookkeeper Workflow

A client sells handmade candles. They buy wax, wicks, and fragrance in bulk. When a candle sells, part of that raw material cost moves from the balance sheet to the income statement as the cost of goods sold. That transfer is inventory accounting in action.

Inventory sits as a current asset until the moment of sale. Most bookkeeping errors in product-based businesses trace back to one of two problems: inventory that was never recorded correctly to start with, or sales posted without a matching COGS entry. Getting this right keeps the balance sheet clean and the margin on the income statement trustworthy.

What is inventory accounting?

Inventory accounting is the process of recording, tracking, and valuing goods held for sale as a current asset on the balance sheet. When goods sell, their cost transfers to cost of goods sold (COGS) on the income statement. Businesses use one of two tracking systems (perpetual or periodic) and one of three costing methods (FIFO, LIFO, or weighted average cost) to determine which cost flows to COGS. For a business carrying 500 SKUs, the choice of method can shift reported profit by thousands of dollars on identical sales.

Key Takeaways

Inventory is a current asset - it sits on the balance sheet until sold, then moves to COGS on the income statement
Two tracking systems exist - perpetual updates inventory in real time with every transaction; periodic waits for a physical count at period end
FIFO assumes oldest units sell first - this matches physical flow for most product businesses and is the most common method
LIFO is rarely used in practice - it's legal only under US GAAP and is almost always a tax-strategy choice
Weighted average cost works well for fungible goods - one pool of cost divided by total units gives a single average cost per unit
Freight-in must be capitalized - shipping costs to receive inventory are part of its cost, not a separate expense

Inventory sits in the same part of the balance sheet as cash and receivables. It's liquid in theory, but only after a sale happens.

What Inventory Accounting Actually Is

Inventory accounting covers every transaction that touches goods you hold for sale. That includes buying goods, receiving them, adjusting for damage or loss, and recording the cost that flows out when a sale happens.

On the balance sheet, inventory is a current asset. The value there represents what you paid (or what it cost to produce) the goods you still hold. The moment a sale happens, that cost leaves inventory and appears on the income statement as cost of goods sold, connecting directly to the COGS article in your chart of accounts.

Two things are always true regardless of which system or method a business uses:

The cost of goods purchased flows into inventory on receipt.
The cost of goods sold flows out of inventory on sale.

Everything else is about how you track the flow and which specific costs you assign to each unit sold.

Perpetual vs Periodic: Two Tracking Systems

Perpetual Inventory

A perpetual system updates the inventory account after every purchase and every sale in real time. When you receive 100 units, inventory goes up by 100. When you sell 10, inventory drops by 10 and COGS goes up by 10. Point-of-sale software, e-commerce platforms, and most modern accounting tools run perpetual tracking by default.

Benefits: you always know what's on hand without counting. The system flags discrepancies. Reports pull current numbers.

Drawback: it requires clean data entry on every transaction. One unrecorded purchase or sale throws the ledger off.

Periodic Inventory

A periodic system doesn't track inventory continuously. Instead, the business physically counts inventory at the end of a period (monthly, quarterly, or annually), then records a journal entry to adjust the inventory balance and calculate COGS for the period.

Periodic COGS formula:

Beginning Inventory + Purchases during period - Ending Inventory (physical count) = COGS

Periodic works for small businesses with few SKUs that don't need real-time inventory visibility. It's simpler to set up but makes it hard to catch shrinkage until the count happens.

Three Costing Methods

The costing method determines which cost you assign to units sold. For fungible goods (wax, grain, wire) you can't actually trace which physical unit left first. The method is a convention, not a literal tracking.

FIFO (First-In, First-Out)

FIFO assumes the oldest inventory sells first. You bought 50 units at $10 in January, then 50 at $12 in March. When you sell 60 units, FIFO says the first 50 came from the January batch ($10) and the last 10 from March ($12). COGS = (50 x $10) + (10 x $12) = $620.

FIFO matches physical flow for most businesses (perishables, fashion, consumer goods). It's the most common method globally.

In a rising-cost environment, FIFO produces lower COGS and higher reported profit compared to LIFO, because older, cheaper costs flow out first.

LIFO (Last-In, First-Out)

LIFO assumes the most recently purchased inventory sells first. Using the same example: COGS under LIFO = (50 x $12) + (10 x $10) = $700.

LIFO produces higher COGS and lower taxable income when costs are rising. That's the main reason US businesses use it. It's not permitted under IFRS (International Financial Reporting Standards), which limits its use to US GAAP companies.

Most small businesses have no reason to use LIFO. If a bookkeeper sees LIFO on the books of a small product company, the first question to ask is whether it was set up intentionally by the CPA or left as a default.

Weighted Average Cost (WAC)

WAC blends all units into one average cost. Take total cost of all inventory on hand, divide by total units, and apply that average cost to every sale until you buy more.

WAC formula:

(Total cost of inventory on hand) / (Total units on hand) = Cost per unit

After each new purchase, recalculate. WAC is practical for fungible goods where unit-level tracking doesn't matter. Fuel, chemicals, and bulk commodities often use WAC.

How Cost Flows to COGS

This is the step that most bookkeepers miss. Recording a sale in the revenue account is only half the journal entry.

When you receive inventory:

Debit: Inventory (asset account increases)
Credit: Accounts Payable (or Cash)

When you sell inventory:

Entry 1 (revenue side): Debit Accounts Receivable / Cash, Credit Revenue
Entry 2 (cost side): Debit COGS, Credit Inventory

If you only record Entry 1, revenue goes up but inventory stays on the balance sheet. Gross margin is inflated. The balance sheet shows an asset that no longer exists. This error compounds every period until a physical count forces a correction.

Modern point-of-sale integrations handle this automatically, but any manual sale or credit memo recorded directly in the accounting software requires both entries.

Period-End Inventory Count and Adjustment

Even with a perpetual system, the book balance and the physical count will differ over time. Shrinkage (theft, damage, evaporation) doesn't get recorded as it happens. Receiving errors, returns processed incorrectly, and data entry mistakes all contribute.

At period end:

Run a physical count.
Compare the count to the book balance.
Record an adjusting journal entry for the difference.

Inventory shrinkage JE:

Debit: COGS (or a separate Inventory Shrinkage expense account)
Credit: Inventory

The debit goes to COGS if shrinkage is a normal cost of sales. Some businesses track it separately to measure it over time.

If the physical count is higher than the book balance (which happens when receipts weren't recorded), the entry reverses: Debit Inventory, Credit COGS or a separate account.

Common Gotchas

Shrinkage never gets booked. A perpetual system can still show phantom inventory if you never reconcile to a physical count. The balance sheet overstates assets; COGS is understated.

Sale recorded without the COGS entry. The revenue hits the income statement but inventory stays on the balance sheet. Gross margin looks too good. Often caught during a balance sheet review when inventory grows despite active selling.

LIFO on books, FIFO on tax (or vice versa). Under US GAAP, the LIFO conformity rule requires that if you use LIFO for tax, you must also use it for financial reporting. Mixing methods is a compliance issue. Check with the CPA before switching.

Freight-in not capitalized. The cost to ship inventory to your location is part of the cost of that inventory. It belongs in the Inventory account, not in a Shipping Expense account. This one is commonly missed by bookkeepers new to product-based businesses.

Receiving inventory without a bill. The inventory hit the dock, but the vendor invoice hasn't arrived. Under accrual accounting, you should debit Inventory and credit Accounts Payable (accrued) on the receipt date, not when the bill arrives.

See also: how fixed assets differ from inventory (both appear on the balance sheet, but fixed assets depreciate instead of flowing to COGS).

How Growthy Handles Inventory Accounting

Most bookkeeping tools treat inventory transactions like any other expense category. Growthy's categorization engine recognizes inventory-related transactions, purchasing patterns, and vendor history. When a transaction matches a prior inventory receipt from the same vendor, Growthy categorizes it to the correct inventory or COGS account and flags it for your review.

You set the rules once. Growthy applies the pattern on future transactions. For bookkeepers managing multiple product-based clients, that means COGS entries don't fall through the cracks between syncs. Learn more at Growthy's features.

Frequently Asked Questions

Is inventory an asset or an expense?

Inventory is a current asset on the balance sheet. It becomes an expense (COGS) on the income statement only when the goods sell. Until then, buying inventory is an asset acquisition, not a period expense. This is why buying a lot of inventory before year-end doesn't reduce taxable income the way buying supplies does.

What's the difference between perpetual and periodic inventory?

Perpetual inventory updates in real time with each purchase and sale. Periodic inventory relies on physical counts at set intervals to calculate what's on hand and what sold. Perpetual is standard for any business using point-of-sale or e-commerce software. Periodic still appears in small cash-based businesses with simple inventory.

Which costing method should a small business use?

FIFO works for most product-based small businesses. It matches physical flow, is accepted globally, and produces a balance sheet inventory value close to current replacement cost. If a CPA has advised LIFO for specific tax reasons, there's a documented reason. Otherwise default to FIFO or WAC depending on whether the business sells distinct units or fungible goods.

Why does gross margin look wrong even when revenue is correct?

The most common cause is a missing COGS entry. Revenue hit the books but inventory never decreased. Check whether every sale has both a revenue entry and a COGS/inventory credit. Also verify that freight-in costs are in the Inventory account, not expensed directly.

What is an inventory shrinkage journal entry?

Shrinkage is the gap between what the books say you own and what's actually on the shelf after a physical count. The adjustment: Debit COGS (or Inventory Shrinkage), Credit Inventory. The amount is the difference in units multiplied by the unit cost under your chosen method.

Inventory accounting is one of those areas where small errors compound quietly across periods. A clean system starts with knowing which tracking method and costing convention you're using, then making sure every receipt and every sale produces the right pair of journal entries.

Start with Growthy to keep inventory and COGS entries in sync across all your product-based clients.