FIFO Cost Basis

What Is FIFO Cost Basis?

FIFO cost basis is a cost basis method that treats the earliest acquired shares as sold first when an investor disposes of identical securities bought in multiple lots. FIFO stands for first in, first out. The earliest lot often has a different basis from later purchases, which can materially change the resulting realized gain or loss.

In many taxable brokerage situations, FIFO acts as the fallback method when the investor does not make an adequate specific identification of another lot.

Key Takeaways

• FIFO treats the earliest purchased shares as the shares sold first.
• It is one form of cost basis method.
• FIFO can create larger or smaller taxable gains depending on how old purchase lots compare with newer ones.
• It often applies when another method is not properly designated.
• The method is especially important in a taxable brokerage account.

How FIFO Cost Basis Works

Suppose an investor bought the same stock in several separate transactions over time. Each lot may have a different cost. Under FIFO, the investor does not get to start with the most convenient lot. Instead, the basis of the earliest shares is assigned first to the sale.

That ordering rule sounds simple, but it can change the tax outcome significantly. In a long-rising stock position, the oldest shares often have the lowest basis, so FIFO can produce a larger taxable gain than a higher-basis lot would have produced.

How FIFO Changes Cost Basis Reporting

FIFO changes the tax outcome because lot ordering determines which basis is matched to a sale. If an investor built a position over many years and sells only part of it, the sale price is only half the story. The other half is which purchase lot is matched to that sale price. FIFO answers that question by matching the sale to the oldest remaining shares first.

This can matter for rebalancing, cash needs, concentrated-position management, and how much capital gains tax the investor recognizes in the current year.

FIFO Versus Specific Identification

The main alternative many investors think about is specific identification. FIFO uses an automatic ordering rule. Specific identification uses the exact lot chosen and documented by the investor.

If no adequate identification is made, FIFO can become the practical default. That is why investors who care about tax control often pay attention before placing the order rather than after the trade confirms.

When FIFO Creates a Bigger Tax Bill

FIFO often produces a bigger gain when the oldest shares were bought at much lower prices than newer ones. If an investor accumulated a stock over time as the price rose, the first shares purchased may have the lowest basis. Selling those shares first can increase the recognized gain even if the investor would have preferred to use a newer, higher-basis lot.

The reverse can also happen. If earlier shares had a higher basis than later ones, FIFO could produce a smaller gain or a larger loss. The point is that FIFO is a rule, not a tax outcome by itself.

Where FIFO Fits in Tax Reporting

FIFO matters most in taxable investing. In a retirement account, current-year sale recognition often does not create the same immediate tax issue. In a taxable account, however, FIFO can directly affect reported gain or loss, after-tax proceeds, and whether a sale fits the investor's broader tax plan.

That is why investors often review broker basis settings and lot-selection procedures before selling appreciated positions.

Example of FIFO Cost Basis

Assume an investor bought 100 shares at $15, another 100 at $30, and another 100 at $45. The investor later sells 100 shares at $50 without specifically identifying a lot. Under FIFO, the $15 lot is generally treated as sold first. That produces a much larger gain than if the investor had sold the $45 lot instead.

The Bottom Line

FIFO cost basis is a method that treats the earliest acquired shares as sold first. It matters because that automatic ordering rule can materially change the gain or loss recognized on a taxable investment sale, especially when the same security was accumulated over time at very different prices.