Selling Shares Bought at Different Prices: Specific Identification vs. FIFO

The direct answer

If you own identical shares purchased at different times and prices, you can generally use specific identification to establish which shares you sold—if the identification satisfies the governing requirements.

If you do not make an adequate identification, ordinary stock generally falls to FIFO: first in, first out.

This decision can change both the amount of gain or loss and whether the transaction is short-term or long-term. And it generally needs to be established as part of the transaction process. You usually cannot wait until tax-return preparation and simply choose whichever historical lot produces the result you prefer.

Why the tax lot matters

Imagine buying the same stock several times:

• one lot when the shares were inexpensive;
• another after the price increased;
• another recently.

Economically, the shares may look identical in the account.

For tax purposes, they are not necessarily interchangeable.

Each lot can have its own:

• adjusted basis;
• acquisition date;
• holding period; and
• unrealized gain or loss.

Identifying the sold lot therefore answers two questions at once:

How much gain or loss did you realize?

and

Was that gain or loss short-term or long-term?

That is why “sell the highest-basis shares” is not automatically a complete tax strategy. A higher-basis lot could also have a different holding period.

What is specific identification?

Specific identification means establishing which particular shares or tax lot were disposed of.

For broker-held shares, Treas. Reg. §1.1012-1(c) is central. Adequate identification generally requires the taxpayer to specify the particular shares through the broker within the governing time and obtain broker confirmation.

The broker record matters because the identification occurs through the custodian. A portfolio screen changed after the transaction is not necessarily evidence that a timely tax identification occurred.

T+1 makes timing more important

Specific identification is not generally an election you first make when preparing Form 8949.

The timing is tied to the transaction and settlement process.

Current Treasury regulations connect the identification deadline to settlement and the time required for settlement under SEC Rule 15c6-1. Standard U.S. securities settlement is generally T+1—one business day after the trade date.

That materially compresses the practical window for dealing with lot identification after a trade.

A standing disposal instruction with a broker can be a strong operational practice and, when valid, can satisfy the identification rules.

But the distinction matters:

Standing instructions can help. They are not legally mandatory in every case.

A taxpayer can still make a valid transaction-specific identification if the regulatory requirements are actually satisfied. The problem with waiting is practical: T+1 leaves very little room to discover after the trade that the broker did not record the intended lot correctly.

What happens if you do not adequately identify the shares?

For ordinary stock, the applicable fallback is generally FIFO.

FIFO means the earliest acquired shares in the relevant account are treated as disposed of first.

That can create a very different result from the investor's intended sale.

It is important not to reverse the rule:

FIFO is generally the fallback. It is not a universal requirement that prevents specific identification.

Similarly, labels such as “HIFO” in a brokerage interface do not create an independent tax-law method. The underlying question remains whether the shares were adequately identified under the governing rules.

Example: same stock, very different tax result

Assume an investor owns:

Lot 1:
100 shares
$20 per-share basis
Long-term

Lot 2:
100 shares
$70 per-share basis
Short-term

The stock is now worth $80 per share, and the investor sells 100 shares.

If Lot 2 is validly identified, the transaction produces:

$8,000 proceeds
− $7,000 basis
\= $1,000 short-term gain

But assume no adequate identification was made and FIFO assigns the older Lot 1:

$8,000 proceeds
− $2,000 basis
\= $6,000 long-term gain

Same company. Same number of shares sold. Same market price.

Different lot. Different basis. Different holding-period character. Different tax result.

Lot identification does not reconstruct missing basis

Suppose your account contains three historical lots but the basis of one of them is missing.

Specific identification does not solve the missing-basis problem.

First determine the legally correct adjusted basis of the position under What If My Cost Basis Is Missing or Wrong?

Then determine which lot was sold under this page.

If the broker's later reporting does not match the legally established result, move to Form 1099-B and Form 8949.

The order matters:

Reconstruct → Identify → Report.

What about average basis?

Average basis is not a universal alternative that can be applied to any stock position.

Special average-basis rules exist for defined eligible holdings, including qualifying regulated investment company shares and certain dividend reinvestment plan stock.

Ordinary corporate shares do not simply become average-basis shares because averaging would make the calculation easier.

The type of security and any applicable election therefore matter before average basis is used.

Separate brokerage accounts matter

Tax lots held through different accounts should not casually be treated as one undifferentiated pool.

The applicable identification framework includes account-level conventions. The account in which the disposition occurs therefore matters when determining the shares associated with that sale.

This is another reason a personal spreadsheet showing all shares across all institutions does not by itself establish the tax lot sold through a particular broker.

What records should you keep?

Useful evidence includes:

• trade and order instructions;
• written or electronic broker confirmations;
• standing disposal instructions, where used;
• lot-level holdings;
• acquisition dates;
• adjusted basis records; and
• records showing changes to the broker's default disposal method.

If securities were transferred between institutions, preserve the transfer and historical lot information as well.

The tax question is not merely what the account displays today. It is whether the identification requirements were satisfied when the disposition occurred.

What if Form 1099-B later shows a different lot?

Do not use the tax return as a place to invent a retroactive identification.

First determine whether there was a legally valid identification at the time of the transaction or whether the applicable fallback controlled.

If a valid identification occurred but the broker's later information reporting differs, the reporting problem belongs in Form 1099-B and Form 8949.

That keeps two different questions separate:

Which shares did tax law treat as sold?

and

How should that result appear on the return?