Inventory Accounting: FIFO, LIFO, and What to Use

Why Inventory Accounting Matters

If you sell physical products — whether you are a retailer, distributor, manufacturer, or contractor who stocks materials — how you account for inventory directly affects your reported profit, your tax bill, and your understanding of business health.

The core question inventory accounting answers: When you sell a product, what was its cost? That sounds simple until you realize you bought the same product at different prices throughout the year. Which cost do you use?

The answer depends on which inventory method you choose. And the choice is not trivial. For a business with $500,000 in annual COGS and rising material prices, the difference between FIFO and LIFO can be $15,000 to $30,000 in taxable income — translating to $4,000 to $9,000 in actual tax difference per year.

The Three Main Methods

FIFO: First In, First Out

FIFO assumes the oldest inventory is sold first. The cost of goods sold reflects the price of the oldest items in stock, and the remaining inventory on your balance sheet reflects the newest (most recent) prices.

Example: You buy 100 widgets in January at $10 each, and 100 more in June at $12 each. You sell 100 widgets. Under FIFO, the cost of those 100 sold is $10 each ($1,000 total), because the January inventory goes out first.

Advantages:

• Matches the physical flow of most businesses (you sell oldest stock first)
• Balance sheet inventory value reflects current market prices
• Generally results in higher reported profit during inflationary periods
• Accepted under both GAAP and IFRS

Disadvantages:

• Higher reported profit means higher taxes when prices are rising
• COGS may not reflect current replacement costs

LIFO: Last In, First Out

LIFO assumes the newest inventory is sold first. COGS reflects the most recent (usually higher) prices, while remaining inventory reflects older (usually lower) prices.

Using the same example: You sell 100 widgets. Under LIFO, the cost is $12 each ($1,200 total), because the June inventory goes out first.

Advantages:

• Lower taxable income during inflation (newer, higher costs reduce profit)
• COGS better reflects current replacement costs
• Tax deferral benefit in periods of rising prices

Disadvantages:

• Balance sheet inventory value may be understated (old prices)
• Not allowed under IFRS (matters if you have international operations)
• Requires maintaining LIFO reserves
• IRS conformity rule: if you use LIFO for taxes, you must also use it for financial reporting

Weighted Average Cost

This method calculates the average cost of all inventory available during the period and uses that average for both COGS and ending inventory.

Using the same example: Total cost: $1,000 + $1,200 = $2,200 for 200 widgets. Average cost: $11 each. Selling 100 widgets = $1,100 COGS.

Advantages:

• Simple to calculate and maintain
• Smooths out price fluctuations
• Good for businesses with large volumes of similar items

Disadvantages:

• Does not reflect actual physical flow
• May not optimize tax position

Side-by-Side Comparison: How Method Choice Affects Your Numbers

Let us trace a full year for a small retailer to see the real dollar impact:

Purchases during the year:

Quarter	Units Purchased	Cost Per Unit	Total Cost
Q1	500	$20.00	$10,000
Q2	500	$22.00	$11,000
Q3	500	$24.00	$12,000
Q4	500	$26.00	$13,000
Total	2,000		$46,000

Sales during the year: 1,500 units at $35 each = $52,500 revenue. 500 units remain in ending inventory.

Method	COGS	Ending Inventory	Gross Profit	Tax at 25%
FIFO	$31,000 (oldest 1,500 units)	$15,000 (newest 500)	$21,500	$5,375
LIFO	$36,000 (newest 1,500 units)	$10,000 (oldest 500)	$16,500	$4,125
Weighted Avg	$34,500 ($23 avg x 1,500)	$11,500 ($23 avg x 500)	$18,000	$4,500

The LIFO vs. FIFO difference: $1,250 in taxes on just $52,500 in revenue. Scale that to $500,000 in revenue and the annual tax difference can reach $10,000 to $15,000.

Which Method Should You Use?

Use FIFO If:

• Prices are stable or declining
• You want your balance sheet to reflect current inventory values
• Your business physically sells oldest stock first (perishables, dated products)
• You want simplicity and GAAP compliance

Use LIFO If:

• Prices are consistently rising
• You want to minimize current tax liability
• You are a US-based business (LIFO is not allowed under IFRS)
• You can maintain the required LIFO reserve calculations

Use Weighted Average If:

• You deal in large quantities of similar, interchangeable items
• Price fluctuations are moderate
• You want the simplest calculation
• Precision between FIFO and LIFO is not critical to your decision-making

Decision Matrix by Business Type

Business Type	Recommended Method	Why
Grocery / Perishable Food	FIFO	Must sell oldest stock first; matches physical flow
Retail Clothing	FIFO or Weighted Average	Seasonal inventory; FIFO matches clearance selling pattern
Hardware / Building Supply	LIFO (if prices rising)	Commodity prices rise consistently; LIFO saves taxes
E-commerce (general)	Weighted Average	High volume, similar items; simplicity wins
Contractor (materials)	Weighted Average or FIFO	Materials used as purchased; average works well
Auto Parts	FIFO	Older parts should sell first; clear dating
Wholesale Distribution	FIFO or LIFO	Depends on price trends in your product category
Manufacturing	Weighted Average	Raw materials blended in production; average most practical

The Tax Implications

The method you choose directly impacts taxable income. In an inflationary environment:

Method	COGS	Gross Profit	Tax Impact
FIFO	Lowest (old prices)	Highest	Higher taxes
LIFO	Highest (new prices)	Lowest	Lower taxes
Weighted Average	Middle	Middle	Middle

Over the long term, total profit recognized is the same under all methods. The difference is timing — which years carry more or less tax burden.

The IRS requires consistency. Once you choose a method, you generally must stick with it. Changing methods requires filing Form 3115 (Application for Change in Accounting Method).

When Prices Are Falling: The Opposite Effect

Everything above assumes inflation (rising prices). But in industries where prices decline (electronics, technology), FIFO actually produces lower taxes because COGS is based on higher old prices and ending inventory reflects lower new prices. Always consider the price direction in your specific industry.

Inventory Management Beyond Accounting

The accounting method is only part of the picture. Good inventory management also requires:

Regular Physical Counts

At least annually, physically count every item in inventory and compare to your records. Shrinkage (theft, damage, miscounts) is real and needs to be identified.

Physical Count Best Practices:

• Schedule the count during a slow period when inventory levels are lowest
• Print your inventory list from accounting software as the starting point
• Use two-person teams: one counts, one records
• Count every location: warehouse, trucks, job sites, showroom
• Investigate all discrepancies before adjusting the books
• Document the count process in case of an audit

Cycle Counting: The Alternative to Annual Counts

Instead of shutting down for a full count once per year, count a portion of your inventory each week:

Week	What to Count
Week 1	High-value items (A items)
Week 2	High-volume items
Week 3	A different section of the warehouse
Week 4	Random sample (10% of remaining items)

Over a quarter, you cover your entire inventory without the disruption of a full count. Most businesses that implement cycle counting discover they catch discrepancies faster and maintain more accurate records year-round.

Inventory Turnover Monitoring

Formula: COGS / Average Inventory

High turnover means inventory is moving quickly. Low turnover means cash is sitting on shelves.

Inventory Turnover Benchmarks

Industry	Good Turnover	Average Turnover	Poor Turnover
Grocery	15 - 25x/year	12 - 15x/year	Under 10x/year
Retail (general)	6 - 10x/year	4 - 6x/year	Under 3x/year
Hardware/Building Supply	5 - 8x/year	3 - 5x/year	Under 3x/year
Wholesale Distribution	8 - 12x/year	6 - 8x/year	Under 5x/year
Auto Parts	4 - 8x/year	3 - 5x/year	Under 3x/year

Days of Inventory on Hand: 365 / Inventory Turnover. This tells you how many days of sales your current inventory represents. If you have 90 days of inventory on hand, that is three months of cash tied up in stock.

Reorder Point Calculation

Know when to reorder based on lead times and sales velocity. Running out of stock loses sales. Overstocking ties up cash.

Reorder Point = (Average Daily Sales x Lead Time in Days) + Safety Stock

Example: You sell 10 units per day. Your supplier takes 14 days to deliver. You keep 5 days of safety stock. Reorder Point = (10 x 14) + (10 x 5) = 140 + 50 = 190 units. When inventory hits 190 units, place an order.

Obsolescence Review

Regularly review inventory for items that are not selling. Obsolete inventory should be written down to net realizable value, not left on the books at full cost pretending it is still worth something.

The ABC Inventory Classification

Not all inventory is created equal. Use ABC classification to focus your attention:

Category	Description	% of SKUs	% of Value	Management Level
A Items	High-value, high-impact	10% - 20%	70% - 80%	Tight control, frequent counts, precise reorder points
B Items	Moderate value	20% - 30%	15% - 25%	Regular monitoring, periodic counts
C Items	Low-value, high-volume	50% - 70%	5% - 10%	Simplified controls, less frequent counts

Focus your management attention on A items. A $50 fastener that sits on the shelf for 6 months is not worth the same attention as a $5,000 specialty tool that you carry 3 of.

The Lower of Cost or Market Rule

Under GAAP, inventory must be reported at the lower of its cost or its market value (net realizable value). If you have inventory that cost $50 per unit but now sells for $30, you must write it down to $30 on your balance sheet.

This prevents your financial statements from overstating asset values. It is not optional.

When to write down inventory:

• Seasonal items after the season ends (holiday inventory in January)
• Damaged or defective items
• Products replaced by newer models
• Items that have not sold in 6 to 12 months
• Products with expired or approaching expiration dates

Example: You have $8,000 in holiday-themed merchandise on January 15. Realistically, it will sell for $3,000 in a clearance sale. You must write it down from $8,000 to $3,000, recognizing a $5,000 loss on your P&L. Leaving it on the books at $8,000 overstates your assets and delays recognizing the loss.

Small Business Exception

Under the Tax Cuts and Jobs Act, businesses with average annual gross receipts of $29 million or less can treat inventory as non-incidental materials and supplies. This means you can deduct inventory costs when purchased rather than when sold. This is a significant simplification for qualifying small businesses. Talk to your accountant about whether this applies to you.

What the Small Business Exception Means in Practice

Without the exception (traditional inventory accounting):

• Buy $50,000 in inventory in November
• Sell $30,000 of it by December 31
• Deduct only $30,000 as COGS this year
• The remaining $20,000 stays as inventory on your balance sheet

With the exception (materials and supplies method):

• Buy $50,000 in inventory in November
• Deduct the entire $50,000 when purchased (or when used/consumed)
• No need to track ending inventory for tax purposes

This simplification eliminates the need for FIFO, LIFO, or weighted average calculations for tax purposes. However, you still need to track inventory for management purposes — knowing what you have on hand and what is selling is essential regardless of tax treatment.

Inventory Software and Technology

Inventory Management Systems

Software	Monthly Cost	Best For	Key Features
QuickBooks Commerce	Included in QBO Plus/Advanced	QBO users with light inventory	Basic inventory tracking, reorder points
Xero (built-in)	Included in all plans	Xero users with simple inventory	FIFO tracking, purchase orders
inFlow	$79 - $439/month	Small wholesalers, manufacturers	Barcode scanning, assembly tracking
Cin7	$349+/month	Multi-channel retail	Warehouse management, EDI, 3PL integration
Sortly	$29 - $74/month	Small businesses, field inventory	Visual inventory, QR codes, mobile app
Fishbowl	$329/month	Manufacturing, QuickBooks integration	Bill of materials, work orders

For most small businesses doing under $2 million in revenue with straightforward inventory, the built-in tracking in QuickBooks or Xero is sufficient. Once you manage multiple warehouses, sell through multiple channels, or need barcode scanning, consider dedicated inventory software.

Inventory KPIs Every Product Business Should Track

KPI	Formula	What It Tells You	Target
Inventory Turnover	COGS / Average Inventory	How fast you sell through stock	Industry-dependent (see benchmarks above)
Days of Inventory on Hand	365 / Inventory Turnover	How many days of supply you carry	30 - 90 days for most businesses
Gross Margin Return on Investment (GMROI)	Gross Margin / Average Inventory Cost	Profit earned per dollar invested in inventory	2.0 or higher ($2 gross profit per $1 in inventory)
Sell-Through Rate	Units Sold / (Units Sold + Ending Inventory)	% of inventory that actually sells	80%+ for fast-moving goods
Shrinkage Rate	(Recorded Inventory - Physical Count) / Recorded Inventory	Loss from theft, damage, and errors	Under 2%
Stockout Rate	Number of stockouts / Total SKUs	How often you run out of items	Under 3%
Carrying Cost as % of Inventory	Total carrying costs / Average inventory value	True cost of holding inventory	20% - 30% per year

The True Cost of Carrying Inventory

Many business owners think inventory just costs what they paid for it. In reality, carrying inventory has significant hidden costs:

Cost Component	Typical Annual % of Inventory Value
Cost of capital (opportunity cost)	8% - 15%
Warehouse/storage space	3% - 8%
Insurance	1% - 3%
Shrinkage (theft, damage, spoilage)	1% - 3%
Obsolescence	2% - 5%
Handling and labor	2% - 5%
Total Carrying Cost	20% - 35%

That means $100,000 in average inventory costs you $20,000 to $35,000 per year just to hold. Every dollar you reduce inventory (without losing sales) saves you 20 to 35 cents annually.

Industry-Specific Inventory Challenges

Retail

• Seasonal buying cycles require large purchases months before the selling season
• Clearance markdowns on unsold seasonal inventory can erase margins
• Multi-location inventory allocation adds complexity

Contractors

• Job-site materials need to be tracked separately from warehouse inventory
• Unused materials from completed jobs should be returned to inventory, not abandoned
• Material price volatility (especially lumber, copper, and steel) requires frequent reorder point recalculation

E-commerce

• Multi-channel selling (website + Amazon + Etsy) requires real-time inventory syncing
• Returns processing must properly add returned items back to available inventory
• Fulfillment center inventory (3PL) must reconcile with your accounting records

Manufacturing

• Raw materials, work-in-progress, and finished goods are three separate inventory categories
• Bill of materials accuracy directly affects COGS calculations
• Waste and scrap must be accounted for as part of production cost

Common Inventory Accounting Mistakes

• Not counting inventory at year-end. Your COGS calculation depends on accurate beginning and ending inventory. If you guess at ending inventory, your profit is wrong.
• Not writing down obsolete inventory. Keeping dead stock at full value on your balance sheet inflates your assets and hides a loss.
• Mixing personal items with business inventory. That case of supplies you bought for a personal project? It should not be in your business inventory count.
• Inconsistent counting methods. If you count items on the shelf but forget about items on trucks, at job sites, or in transit, your count is wrong.
• Not accounting for shrinkage. The difference between what your records say you should have and what you actually have is shrinkage. Average retail shrinkage is about 1.4% of revenue. In some industries, it is much higher.
• Changing methods without filing Form 3115. Switching from FIFO to LIFO (or vice versa) requires IRS approval. Doing it without filing can trigger penalties.
• Ignoring landed cost. The true cost of inventory includes the purchase price plus shipping, customs, duties, and handling. If you only record the purchase price, your COGS is understated and your margins look better than they are.

The Bottom Line

Inventory accounting is not just record keeping. It is a tax strategy and a management tool. Choose the method that matches your business reality and tax goals, maintain accurate records, and review inventory health regularly. The wrong method quietly costs you money through higher taxes or misleading financial statements. The right method, consistently applied, gives you control.