The Complete Guide To FIFO And LIFO Inventory Costing

When purchase prices change, FIFO and LIFO can turn the same physical inventory activity into different cost of goods sold, gross profit, and ending inventory amounts. The choice is not only a year-end calculation. It affects how the accounting team maintains cost layers, explains results, prepares tax filings, and documents controls.

FIFO uses the oldest inventory costs first, while LIFO uses the newest inventory costs first. This guide compares both methods, works one rising-cost ledger from start to finish, and gives you a practical checklist for choosing and documenting the method. The examples are educational and hypothetical; your tax adviser and financial-reporting adviser should confirm the rules that apply to your business.

What Is the Difference Between FIFO and LIFO?

Inventory costing answers a narrow but important question: which costs move from inventory to cost of goods sold when units are sold? It does not necessarily tell warehouse staff which physical carton to ship. A company can rotate perishable stock using first-in, first-out operationally while applying an approved accounting cost-flow method to its records.

The IRS explains that FIFO assumes the items purchased or produced first are the first items sold, consumed, or otherwise disposed of, while LIFO assumes the items purchased or produced last are disposed of first. The remaining costs become ending inventory. See the IRS inventory-method guidance in Publication 538.

Decision point	FIFO	LIFO
Costs assigned to sales first	Oldest cost layers	Newest cost layers
Costs commonly left in ending inventory when prices rise	Newer, higher costs	Older, lower costs
COGS in the rising-cost example below	Lower	Higher
Recordkeeping focus	Preserve newer layers	Preserve and monitor older layers
U.S. tax adoption step	Document the selected method and apply it consistently	Coordinate Form 970, conformity, layers, and change controls

Neither method changes the number of units physically purchased or sold. The methods allocate the same cost of goods available for sale between expense and the balance sheet in different ways. That distinction is why a controller should separate the warehouse rotation rule from the accounting cost-flow rule in the written policy.

How Do FIFO and LIFO Change COGS and Ending Inventory?

The basic relationship is straightforward. Beginning inventory plus purchases and other capitalized inventory costs create goods available for sale. Ending inventory remains on the balance sheet, and the rest becomes cost of goods sold. IRS Publication 334 states that subtracting closing inventory from the cost of goods available for sale gives cost of goods sold for the tax year. See the IRS Tax Guide for Small Business.

Price movement determines the direction of the FIFO versus LIFO difference. When prices rise, the IRS says LIFO produces a larger cost of goods sold and a lower closing inventory, while FIFO produces a lower cost of goods sold and a higher closing inventory. When prices fall, the relationship reverses. The size of the effect depends on quantities sold, the spread between cost layers, and the inventory remaining at period end.

• Higher COGS reduces gross profit before other income and expenses.
• Lower ending inventory reduces the inventory asset shown on the balance sheet.
• A larger cost spread creates a larger difference between the methods when the sales quantity reaches multiple layers.
• No price change means identical unit costs, so FIFO and LIFO produce the same result for the affected units.

This is a timing and allocation effect, not a second source of economic cost. An accounting control should therefore prove that COGS plus ending inventory reconciles to the total available cost under either method. The control is simple enough to repeat every close and useful enough to catch missing layers, duplicate quantities, and formula errors.

How Do You Calculate FIFO and LIFO?

Assume a small distributor buys one identical item in three batches. The company sells 180 units for $25 each before period end. There is no opening inventory, purchase freight, shrinkage, return, rebate, or other capitalization adjustment in this simplified example.

Purchase layer	Units	Unit cost	Layer cost
January	100	$10	$1,000
March	100	$12	$1,200
June	100	$14	$1,400
Total available	300		$3,600

Sales revenue is 180 units multiplied by $25, or $4,500. Both methods begin with the same 300 units and $3,600 of cost. They differ only in which cost layers are assigned to the 180 units sold.

FIFO Calculation

• Use all 100 January units at $10: $1,000.
• Use 80 of the March units at $12: $960.
• FIFO COGS is $1,960.
• Ending inventory is 20 March units at $12 plus 100 June units at $14: $1,640.
• Gross profit is $4,500 revenue minus $1,960 COGS: $2,540.

The FIFO inventory method leaves the latest costs in ending inventory. In this example, the balance-sheet amount reflects the $12 and $14 layers, while the $10 layer has already moved through COGS.

LIFO Calculation

• Use all 100 June units at $14: $1,400.
• Use 80 of the March units at $12: $960.
• LIFO COGS is $2,360.
• Ending inventory is 20 March units at $12 plus 100 January units at $10: $1,240.
• Gross profit is $4,500 revenue minus $2,360 COGS: $2,140.

Result	FIFO	LIFO	Difference
COGS	$1,960	$2,360	LIFO is $400 higher
Ending inventory	$1,640	$1,240	FIFO is $400 higher
Gross profit	$2,540	$2,140	FIFO is $400 higher

The example contains a useful control check: COGS plus ending inventory must equal the $3,600 cost of goods available for sale. FIFO produces $1,960 plus $1,640. LIFO produces $2,360 plus $1,240. Both total $3,600, so the comparison changes allocation, not total available cost.

A real calculation needs more inputs than this teaching ledger. The policy should specify how the company handles freight-in, purchase discounts, returns, rebates, manufacturing overhead, standard-cost variances, backdated receipts, negative inventory, and damaged or obsolete goods. The layer report should tie to the inventory subledger and the subledger should reconcile to the general ledger.

When Should a Business Consider FIFO or LIFO?

Start with the business task, not a desired profit number. The right question is whether the method can be applied consistently, supported by the reporting framework and tax position, and reproduced from reliable source data. Management should understand the effects, but it should not select layers after seeing the result.

Consider FIFO When the Team Needs Simpler Layers

FIFO is often easier for a small accounting team to explain because older layers clear first and ending inventory contains more recent costs. It can align naturally with physical rotation for dated or perishable goods, although the physical flow and accounting assumption remain separate. The team still needs reliable receipts, quantities, landed costs, adjustments, and close controls.

Consider LIFO Only With the Full Commitment Visible

LIFO may deserve analysis when an eligible U.S. business carries material inventory, experiences meaningful cost inflation, can maintain layers or pools, and has advisers who can evaluate the tax and reporting consequences. Do not compare only the current-year tax effect. Include implementation work, continuing calculations, liquidation risk, reporting coordination, and the cost of changing methods later.

Use a Decision Memo

• Describe the inventory population and current physical flow.
• Quantify at least one normal-cost, rising-cost, and falling-cost scenario.
• Identify the applicable reporting and tax requirements with adviser input.
• Estimate system, data, reconciliation, and review effort.
• List the statements, lender packages, owner reports, and tax filings affected.
• Name the policy owner, calculation preparer, reviewer, and change approver.
• Record the decision, effective date, and retained supporting documents.

This memo prevents a later reviewer from reconstructing management’s reasoning from journal entries alone. It also gives the controller a stable baseline for assessing whether a business change, acquisition, new inventory system, or significant cost shift requires renewed advice.

What Does Electing LIFO Commit You To?

LIFO is not a switch to flip after management sees the year-end result. Adoption involves a tax election, continuing layer calculations, financial-reporting coordination, and controlled method changes.

1. Prepare the election. IRS Publication 538 says a taxpayer adopts LIFO by filing Form 970, or a statement containing all information required on the form, with the timely filed return for the first year LIFO is used. The IRS Form 970 page identifies the form as the election to use LIFO under Internal Revenue Code section 472.
2. Review book conformity before filing. The current Form 970 asks whether the applicant or a financially related corporation issued credit statements or reports and, if so, which inventory methods were used to determine income, profit, or loss. Give the full reporting package to the tax adviser rather than treating LIFO as an isolated tax return choice.
3. Maintain layers or pools. Define the source data, period cutoffs, cost components, pool structure if applicable, index source, calculation owner, and reviewer.
4. Monitor liquidations. Add a review that compares current purchases, unit sales, and layer reductions before close approval.
5. Maintain a method bridge. If the business tracks a LIFO reserve for management or financial-reporting purposes, define the calculation, reconciliation, disclosure decision, and reviewer. In the worked example, FIFO inventory of $1,640 minus LIFO inventory of $1,240 creates a $400 bridge.
6. Control future changes. IRS Publication 334 says a business that wants to change its inventory accounting method files Form 3115. Route any proposed change through tax, reporting, and approval review before entries are posted.

The checklist is intentionally operational. Form filing alone does not create reliable inventory accounting. The method must be reflected in the subledger, close procedures, review evidence, statement preparation, and record retention. Keep the election, adviser instructions, calculation workpapers, approval evidence, and any method-change filings together.

What Are the LIFO Reserve, LIFO Liquidation, and Dollar-Value LIFO?

LIFO Reserve

A LIFO reserve is a bridge between inventory measured under LIFO and the same inventory measured under another stated basis, commonly FIFO. In the worked example, the reserve-like difference is $400. A policy should define the comparison basis, sign convention, source reports, reconciliation frequency, journal-entry treatment if any, disclosure owner, and reviewer.

LIFO Liquidation

A LIFO liquidation occurs when current sales draw down older LIFO cost layers because replacement purchases do not maintain the quantity represented by those layers. The practical risk is that old costs can enter current COGS and distort comparisons with a normal replenishment year. The close checklist should flag reductions in layer quantities before management approves financial results.

Dollar-Value LIFO

Dollar-value LIFO groups goods into pools and measures changes in the pool’s dollar value rather than tracking each unit as a separate layer. IRS Publication 538 explains that goods and products are grouped into one or more pools under dollar-value LIFO and describes a simplified method using appropriate government price indexes. A business considering this approach needs qualified advice on pool design, indexes, base-year cost, and annual calculations.

How Should You Write the Method Into an Accounting Policy?

The policy should be short enough to use and specific enough to test. Place it with the company’s other accounting methods, then connect it to inventory count, purchasing, receiving, adjustment, and month-end close procedures.

Sample Policy Language

Inventory costing policy: The company values eligible inventory using the [FIFO or LIFO] cost-flow method. The inventory accountant maintains cost layers from approved receiving and purchasing records, reconciles the inventory subledger to the general ledger each month, and documents all manual adjustments. The controller reviews quantity exceptions, obsolete or damaged items, layer changes, and the period-end valuation before approving the close. Any proposed method change requires written approval from the controller and the company’s tax and financial-reporting advisers before implementation.

If the company uses LIFO, add the election year, Form 970 retention location, conformity review, pool and index rules if applicable, liquidation monitoring, reserve bridge responsibility, and escalation thresholds. If it uses FIFO, identify the source of purchase-layer costs, treatment of landed costs and returns, and the procedure for resolving negative inventory or backdated transactions.

Minimum Control Evidence

• Approved policy, selected method, scope, and effective date.
• Inventory subledger to general-ledger reconciliation.
• Purchase-layer or pool report tied to source documents.
• Physical-count variance review and approved adjustments.
• Obsolescence, damage, returns, and negative-inventory review.
• FIFO and LIFO bridge when management uses both views.
• LIFO liquidation review when applicable.
• Controller signoff and retained tax-adviser instructions.

A Repeatable Period-End Procedure

1. Freeze the cutoff. Confirm the last receiving, shipping, transfer, and adjustment documents included in the period. Investigate backdated transactions before running the layer report.
2. Reconcile quantities. Compare the perpetual inventory, physical-count results, and approved variance adjustments. A cost-flow calculation cannot correct an unsupported quantity.
3. Validate costs. Tie sampled unit costs to purchase invoices, receiving records, freight allocations, production records, or other approved source documents. Review negative costs and unusual overrides.
4. Run the selected method. Apply FIFO or LIFO to the approved quantity and cost data. Retain the detailed layer or pool report, not only the summary journal entry.
5. Perform the control proof. Confirm that COGS plus ending inventory equals goods available for sale. Reconcile the result to the general ledger and explain every difference.
6. Review special items. Evaluate obsolescence, damage, returns, consignment goods, goods in transit, and LIFO liquidations where applicable. Keep these decisions separate from the ordinary layer calculation.
7. Approve and lock. The controller reviews the reconciliation, exceptions, and financial-statement effect before posting or approving the final entry. Restrict later changes to an approved reopening process.

This procedure gives the policy an observable control trail. A reviewer can trace the result from physical quantities and source costs through the chosen method to the journal entry. If the business changes systems, locations, product lines, or advisers, the same evidence also helps the next team distinguish a data problem from a method problem.

The final decision should make the records easier to explain, not merely change the reported answer. A repeatable policy lets a new bookkeeper reproduce the calculation, gives the controller evidence to review, and helps advisers see whether the tax return and financial statements use the intended method.

Frequently Asked Questions

What Is the Main Difference Between FIFO and LIFO?

FIFO assigns the oldest inventory costs to sales first. LIFO assigns the newest inventory costs to sales first. The remaining cost layers determine ending inventory.

Which Method Reports Higher Profit When Costs Rise?

FIFO generally reports higher gross profit when costs rise because older, lower costs enter COGS first. The actual difference depends on purchase prices, quantities sold, and available layers.

Does LIFO Mean the Newest Physical Goods Must Ship First?

No. LIFO is a cost-flow assumption. A warehouse can rotate physical goods according to shelf life, lot control, or operating policy while accounting assigns costs under the approved method.

What Is a LIFO Reserve?

A LIFO reserve is the difference between inventory measured under another stated basis, commonly FIFO, and inventory measured under LIFO. It helps users bridge the effect of the cost-flow method when the calculation and reporting basis are clearly defined.

Can a Business Switch From FIFO to LIFO Whenever It Wants?

No. Adopting LIFO involves Form 970 and related requirements, while later inventory accounting-method changes require formal tax review and generally use Form 3115. Obtain adviser approval before changing the ledger or return treatment.