FIFO vs LIFO: Which Inventory Valuation Method Is Right for Your Shopify Store?

When you sell a product, which unit did you just sell?

You know the answer physically — it is the one you picked from the shelf. But for accounting and tax purposes, the answer is not obvious. Your 200 units of that product may have been purchased at three different prices over the past year. Which cost do you use to calculate your profit margin?

This is the FIFO vs LIFO question. And the method you choose has real consequences for your reported profit, your tax liability, and how you understand your margins.

The Core Concept

Imagine you buy 100 units of a product in January at £10 each, then 100 more in March at £12 each. You now have 200 units: 100 at £10 and 100 at £12.

In April, you sell 80 units. What is your cost of goods sold (COGS)?

• Under FIFO: You sold the 80 oldest units (January batch at £10). COGS = £800.
• Under LIFO: You sold the 80 newest units (March batch at £12). COGS = £960.
• Under Average Cost: You use the weighted average: ((100 × £10) + (100 × £12)) / 200 = £11/unit. COGS = £880.

The physical stock does not change. But your reported profit changes by £160 depending on the method. Your gross margin changes. Your tax bill changes. Same business, same operations, different numbers on paper.

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FIFO (First In, First Out)

Under FIFO, the cost assigned to goods sold is the cost of the oldest inventory first.

The intuition: You are assuming you sell your oldest stock first — which is also what most well-run ecommerce businesses actually do physically. FIFO accounting matches physical reality in most cases.

FIFO in an inflationary environment

When supplier costs are rising (which is most of the time), FIFO produces: - Lower COGS (older, cheaper inventory is expensed first) - Higher reported gross profit - Higher taxable income - Higher balance sheet inventory value (remaining stock is valued at more recent, higher prices)

FIFO in a deflationary environment

When costs are falling: - Higher COGS (older, more expensive stock expensed first) - Lower reported gross profit - Lower taxable income

When to use FIFO

• You are based in the UK, EU, or any IFRS jurisdiction (FIFO is effectively mandatory)
• You have perishable or time-sensitive products (FIFO matches physical best practice)
• You want your inventory balance sheet value to reflect current replacement costs

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LIFO (Last In, First Out)

Under LIFO, the cost assigned to goods sold is the cost of the most recently purchased inventory first.

The intuition: You are assuming you sell your newest stock first. Physically unusual for most ecommerce operations.

LIFO in an inflationary environment

When costs are rising, LIFO produces: - Higher COGS (recent, more expensive purchases expensed first) - Lower reported gross profit - Lower taxable income — this is the primary reason LIFO exists as a method - Lower balance sheet inventory value (remaining stock is valued at older, lower prices)

The LIFO reserve

If you use LIFO for a long time in an inflationary environment, your balance sheet inventory value becomes increasingly understated relative to replacement cost. The gap between LIFO value and FIFO value is called the LIFO reserve — and sophisticated analysts always add it back when assessing a business.

When to use LIFO

LIFO is only permitted under US GAAP. If you are based in the UK, EU, or any country using IFRS, you cannot use LIFO. If you are a US-based business and your primary goal is to minimise current-period tax liability in an inflationary environment, LIFO may be worth discussing with your accountant.

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Weighted Average Cost (WAC)

A third method worth understanding: WAC calculates a new average cost every time you receive inventory, and assigns that average to all units sold.

Formula: (Total inventory value) / (Total units on hand) = average cost per unit

In the earlier example: ((100 × £10) + (100 × £12)) / 200 = £11 per unit

When WAC makes sense

• You have high transaction volumes and many small purchases
• Products are fungible (identical units from different batches)
• You want to smooth the volatility of FIFO vs LIFO swings across periods

WAC is more administratively simple than FIFO or LIFO for businesses with frequent small replenishments, and it is permitted under both IFRS and US GAAP.

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The Practical Impact: A Side-by-Side Example

Scenario: You start with 100 units bought at £10, receive 100 more at £14, then sell 150 units at £20 each.

FIFO: reports £200 more profit, £200 more in inventory. Higher tax liability. LIFO: reports £200 less profit, £200 less in inventory. Lower tax liability (US only). WAC: splits the difference.

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What Shopify Uses by Default

Shopify tracks inventory quantities but does not natively calculate COGS using a specific cost method. The cost you enter per product in Shopify is the cost used in Shopify's margin reports — it does not automatically update when you receive new inventory at different prices.

For accurate COGS calculation under FIFO, WAC, or any other method, you need either:

1. A third-party inventory/accounting app that maintains a proper cost layer (e.g., A2X, Xero with inventory tracking, or an IMS that pushes cost to your accounting system)
2. A manual COGS calculation in your accounting software using exported Shopify sales data

CoreCaptain maintains cost per SKU and allows you to configure your cost calculation method — including using actual cost data imported via CSV or a percentage-of-price estimate — so margin calculations in your analytics reflect your real economics rather than a rough approximation.

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Which Method Should You Use?

If you are in the UK, EU, or an IFRS country: FIFO or WAC. LIFO is not permitted.

If you are in the US: FIFO is simpler and more intuitive. LIFO provides a tax deferral benefit in inflationary periods but adds administrative complexity and is banned under international standards.

If you have frequent, small replenishments: WAC reduces volatility in your reported margins.

If you have products with significant cost fluctuation: FIFO reflects the most current replacement cost on your balance sheet.

If you are just starting out: Use FIFO. It matches physical reality, is internationally accepted, and is what your accountant will expect.

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Summary

FIFO, LIFO, and WAC are three answers to the same question: which cost do I assign to the units I just sold? They produce different profit figures, different tax outcomes, and different balance sheet inventory values from identical underlying operations.

FIFO is the most widely used, internationally accepted, and operationally intuitive. For most Shopify merchants, it is the right default.

Whichever method you choose: be consistent. Changing cost methods mid-year requires a restatement and creates comparability problems in your financials. Pick one, document it, and stick with it.