Cost Basis Methods: FIFO, Specific ID, and Average Cost

The three cost basis methods available to most investors are first-in, first-out (FIFO), specific identification, and average cost. FIFO is the default and assumes your oldest shares are sold first. Specific identification lets you name the exact lot you want to sell, which gives you the most control over the taxable gain or loss you report. Average cost pools every share of a mutual fund, ETF, or dividend reinvestment plan holding into a single uniform basis. The same sale can produce very different tax bills under each one, so the method you use is a real decision, not a formality.

FIFO: The Default

FIFO treats your earliest-purchased shares as the first ones sold. Buy 100 shares in January and another 100 in June, sell 100 in October, and FIFO assigns the January lot to that sale automatically. You don’t have to elect it or tell your broker anything. Treasury regulations under 26 U.S.C. § 1012 make FIFO the default whenever you haven’t chosen something else.¹

Because it reaches for your oldest shares, FIFO usually produces long-term capital gain treatment, which is the favorable side of the rate structure. Anything held more than a year qualifies for long-term rates of 0%, 15%, or 20%. Anything held a year or less is taxed as ordinary income, which can be close to double.²

The trade-off in a rising market is that your oldest shares tend to be your cheapest, so FIFO also tends to maximize the size of the gain. You get the better rate applied to a bigger number. FIFO fits investors who buy and hold and don’t want to think about lot-level decisions. It fits poorly when you’ve accumulated shares across a wide range of prices and want to steer the tax outcome of a specific sale.

Specific Identification: The Method With Control

Specific identification lets you pick the exact lot to sell, identified by its purchase date and price. If you own 500 shares bought across five dates at five prices, you choose. Sell the highest-cost lot and you shrink the gain. Sell an underwater lot and you harvest a loss. This is the only method that gives you direct control over which piece of your position hits your tax return.

Timing is the requirement that trips people up. You must identify the shares no later than the trade’s settlement, and your broker must confirm the selection back to you within a reasonable time.¹ Miss that window and the sale falls back to FIFO. Most brokerages now let you select a lot at the moment you place the order, so the mechanics are easier than they once were, but you still have to make the choice before you sell.

Standing Instructions and HIFO

You don’t have to pick lots by hand every time. Most brokerages let you set a standing tax lot method on your account. Highest-in, first-out (HIFO) automatically sells your most expensive shares first, minimizing gains. Last-in, first-out (LIFO) sells your most recent purchases first. Some brokers offer variations that prioritize long-term or short-term lots. If you don’t set anything, the account defaults to FIFO.

Standing instructions are a form of specific identification, with the broker applying your rule for you. You can still override the standing method on any single trade. That combination — set HIFO by default, override when a different lot makes sense — is where a lot of tax-conscious investors settle.

Recordkeeping

Specific identification comes with a paper trail requirement. Your broker’s written confirmation of the lot you selected is the evidence that supports what you reported. Without that contemporaneous record, you lose the ability to claim you sold any particular lot. Keep trade confirmations and year-end statements for at least three years after filing the return that reports the sale, longer if the position involves complicated basis adjustments.

Average Cost: For Funds and DRIPs

Average cost divides your total dollars invested by your total shares, giving every share the same basis. Put $10,000 into a fund over time and hold 200 shares, and your basis is $50 per share on every sale.

Average cost is available for mutual funds, most ETFs (which are typically structured as regulated investment companies), and shares in a dividend reinvestment plan. It is not available for individual stocks held outside a DRIP.¹ For someone making monthly contributions to an index fund, the method eliminates the burden of tracking dozens of small lots, which is why it dominates automated investment plans.

The catch is the lock-in. Once you use average cost for a holding, you’re stuck with it for that security until you revoke the election in writing before your next sale. Shares acquired while the election was in effect keep their averaged basis even after you switch to another method. Only shares purchased after the change get tracked under the new method. Average cost is easy to elect and hard to unwind cleanly, so think it through before you use it.

Why the Method You Choose Moves Real Dollars

The reason this isn’t just accounting comes down to the rate gap. Long-term capital gains face rates of 0%, 15%, or 20% depending on income. Most filers land in the 15% bracket. The 20% rate applies at higher incomes (roughly above $545,000 for single filers or $613,700 for married couples filing jointly).² Short-term gains have no preferential rate. They’re taxed as ordinary income, and the spread between the two can easily be 15 to 20 percentage points on the same dollar.

Higher earners face another layer. The 3.8% Net Investment Income Tax applies to capital gains once modified adjusted gross income clears $200,000 for single filers or $250,000 for married couples filing jointly.³ That pushes the effective top long-term rate to 23.8%. A method that consistently sells higher-cost lots or steers around short-term treatment can save real money across the life of a portfolio.

When These Methods Don’t Apply

Not every position works off a basis you chose. A few situations override the method question entirely, and assuming FIFO or HIFO controls when it doesn’t is an expensive mistake.

Inherited assets receive a stepped-up basis equal to fair market value on the date the original owner died, or on an alternate valuation date six months later if the executor elects it. Your basis cannot exceed the value reported for estate tax purposes.⁴

Gifted assets carry over the donor’s original basis. If your uncle paid $20,000 for shares now worth $50,000 and gifts them to you, your basis is $20,000.⁵ If the shares are worth less than the donor’s basis at the time of the gift, a dual-basis rule kicks in: the donor’s basis for measuring a gain, the lower gift-date value for measuring a loss, and no gain or loss at all if you sell between the two.

Wash sales also override your method. Sell at a loss and buy a substantially identical security within 30 days before or after the sale, and the loss is disallowed for that year. It gets added to the basis of the replacement shares instead, deferring the deduction until you sell them.⁶ Dividend reinvestment inside the 30-day window is a common accidental trigger. Brokers track wash sales within a single account, but trades split across a taxable account and an IRA can create wash sales your broker won’t flag.

Corporate actions reshape basis without any sale on your part. A 2-for-1 stock split turns 100 shares at $30 into 200 at $15; total basis is unchanged.⁷ Tax-free spinoffs require you to split your original basis between parent and new company by relative market value on the first day of separate trading. Digital assets get their own reporting regime starting January 1, 2026, with brokers reporting basis on Form 1099-DA; FIFO and specific identification apply, and average cost applies where the asset qualifies.⁸

Reporting the Method You Used

Choosing a method doesn’t finish the job. The number has to land on your return in a way the IRS can match.

Securities are split into covered and noncovered. For covered securities, your broker reports basis to both you and the IRS on Form 1099-B. For noncovered securities, the broker sends basis only to you, and calculating and reporting it is your responsibility.⁹ The dividing line depends on when the security was acquired:

Individual stocks: covered if purchased on or after January 1, 2011
Mutual funds, ETFs, and DRIP shares: covered if purchased on or after January 1, 2012
Most bonds and options: covered if purchased on or after January 1, 2014
More complex bonds: covered if purchased on or after January 1, 2016

Older positions need your own records. The broker may show a basis figure for reference, but the IRS won’t have that number and won’t know if you report something else.

Every taxable sale flows through Form 8949, which lists each transaction with dates, proceeds, basis, and any adjustments for wash sales or corrections. Totals carry to Schedule D, where the tax is calculated.¹⁰ For covered securities where the 1099-B matches what you’re reporting, summary reporting on Schedule D is sometimes allowed. Any adjustment to a broker-reported basis figure has to be shown on Form 8949.

Mismatches between the 1099-B and the return are one of the most common automated audit triggers. The accuracy-related penalty for negligence or substantial understatement is 20% of the underpaid tax, plus interest from the original due date.¹¹ Trade confirmations and year-end statements are what you use to defend the numbers you reported.

1
eCFR. 26 CFR 1.1012-1 – Basis of Property
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Internal Revenue Service. Topic No. 409, Capital Gains and Losses
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Internal Revenue Service. Net Investment Income Tax
4
Office of the Law Revision Counsel. 26 USC 1014 – Basis of Property Acquired From a Decedent
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Office of the Law Revision Counsel. 26 USC 1015 – Basis of Property Acquired by Gifts and Transfers in Trust
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Office of the Law Revision Counsel. 26 USC 1091 – Loss From Wash Sales of Stock or Securities
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Internal Revenue Service. Stocks (Options, Splits, Traders) 7
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Internal Revenue Service. Digital Assets
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Internal Revenue Service. Instructions for Form 1099-B (2026)
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Internal Revenue Service. Instructions for Form 8949 (2025)
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Office of the Law Revision Counsel. 26 USC 6662 – Imposition of Accuracy-Related Penalty on Underpayments