Understanding FIFO Inventory Valuation
The first-in, first-out method reflects the natural flow of stock for most retail and manufacturing businesses. When inventory is acquired at different prices over time—whether due to market fluctuations, supplier changes, or seasonal pricing—accountants must track each batch separately.
Under FIFO, when units are sold, they are assumed to come from the oldest purchase first. If a company bought 100 units at £10 in January and 50 units at £12 in February, and then sold 120 units, FIFO assumes all 100 January units were sold (at £10 each) plus 20 of the February units (at £12 each). The remaining 30 February units stay on the balance sheet at £12 per unit.
FIFO is legally required or strongly preferred in many jurisdictions, and it mirrors actual stock rotation in warehouses. Unlike LIFO (last-in, first-out) or weighted-average methods, FIFO leaves the most recent, typically more expensive purchases in ending inventory—an important distinction when prices are rising or falling.
FIFO Calculation Formulas
Two core calculations drive FIFO inventory accounting:
1. Total inventory value is the sum of all purchases (units × price per batch).
2. Cost of goods sold (COGS) is calculated by removing sold units from inventory in purchase order, using the cost of each batch as units are depleted.
3. Revenue is generated from the number of units sold at the selling price per unit.
Revenue = Units Sold × Selling Price per Unit
Ending Inventory Value = (Remaining Units from Batch 1 × Price 1) + (Remaining Units from Batch 2 × Price 2) + ... + (Remaining Units from Batch N × Price N)
COGS = (Units Sold from Batch 1 × Price 1) + (Units Sold from Batch 2 × Price 2) + ... + (Units Sold from Batch N × Price N)
Units Sold— Total number of units sold during the accounting periodSelling Price per Unit— Revenue per unit sold to customersBatch n (Price & Quantity)— Unit cost and quantity for each separate inventory purchase
How Inflation and Deflation Impact FIFO Results
Price changes fundamentally alter the financial picture under FIFO. In an inflationary environment, where acquisition costs rise over time, FIFO leaves the most expensive inventory on the balance sheet. This inflates the ending inventory value compared to other methods—a substantial advantage if your goal is to show stronger asset positions. Conversely, COGS is lower because earlier, cheaper purchases are expensed first, which boosts reported profit and increases tax liability.
Deflation reverses these effects. As prices fall, older inventory becomes relatively costly compared to recent purchases. Under FIFO, those expensive early batches are sold first, pushing COGS higher and squeezing profit margins. The ending inventory value looks artificially low because it holds only the cheapest recent purchases.
This sensitivity to price trends means FIFO results can obscure operational reality. Financial analysts comparing companies across inflationary and deflationary periods may draw misleading conclusions about inventory management efficiency or profitability trends.
FIFO's Effect on Tax Liability and Financial Ratios
Because COGS reduces taxable income, the way you value inventory directly affects how much tax you owe. A higher COGS figure (from expensive batches) reduces taxable profit and lowers tax bills. A lower COGS (from cheaper batches) increases reported profit and increases taxes.
FIFO also distorts key financial metrics. The current ratio (current assets ÷ current liabilities) shifts based on ending inventory value. Inventory turnover, days inventory outstanding, return on assets, and the cash conversion cycle all hinge on the inventory figure. In inflationary periods, FIFO makes these ratios look better than they might under other methods—a factor that savvy investors and creditors must account for when analyzing financial statements.
The relationship is especially relevant for seasonal businesses or those with volatile input costs, where batch-by-batch tracking reveals true economic performance versus inflated or deflated figures from averaging methods.
FIFO Calculation Best Practices
Accurate FIFO calculations require careful attention to purchase order sequencing and unit tracking.
- Track purchases chronologically — Record each purchase as a separate batch with its date, quantity, and unit cost. Mixing up the sequence undermines the entire FIFO calculation. If you later discover a prior-period purchase was misrecorded, adjust both ending inventory and COGS retroactively to avoid financial statement errors.
- Monitor unit availability before selling — Verify that total units purchased exceed units sold. Overselling (reporting more units sold than acquired) creates negative inventory and signals data entry errors. Implement an inventory count reconciliation before finalizing COGS each period.
- Watch for price volatility in multi-batch scenarios — When you have many purchase batches at significantly different prices, a small change in the quantity sold can shift COGS by hundreds or thousands of pounds. Review COGS calculations carefully, especially near batch boundaries, to ensure accuracy.
- Reconcile FIFO results to perpetual inventory records — FIFO assumes goods are removed in order, but real warehouses may not follow that sequence. Periodically verify that the FIFO calculation matches your physical stock rotation and cycle counts to catch discrepancies early.