Tax Loss Harvesting: Using Investment Losses Strategically

Tax loss harvesting is the practice of selling investments at a loss to offset capital gains and reduce your tax bill. When done strategically, it allows you to maintain your investment exposure while generating tax benefits. This technique is used by individual investors and automated by many robo-advisors. The key is understanding the rules, especially the wash sale rule, to avoid disqualification.

How It Works

When you sell an investment for less than you paid, you realize a capital loss. Capital losses first offset capital gains dollar for dollar. Short-term losses offset short-term gains, and long-term losses offset long-term gains. Any remaining losses can offset up to 3,000 dollars of ordinary income per year. Losses beyond that carry forward indefinitely to future tax years. This makes every realized loss a future tax benefit.

The Wash Sale Rule

The IRS wash sale rule prevents you from claiming a loss if you buy a substantially identical security within 30 days before or after the sale. This 61-day window is strictly enforced. If you trigger a wash sale, the disallowed loss is added to the cost basis of the replacement shares. To avoid it, you can wait 31 days to repurchase, buy a similar but not identical investment like a different index fund tracking the same market, or invest the proceeds in a different asset class entirely.

Practical Strategy

• Review your portfolio quarterly for loss harvesting opportunities
• Prioritize harvesting short-term losses as they offset income taxed at higher rates
• Replace sold positions with similar but not identical investments to maintain portfolio allocation
• Track your wash sale window carefully across all accounts including IRAs
• Carry forward unused losses and use them to offset gains in future years

When Not to Harvest Losses

Tax loss harvesting is not always beneficial. If you are in a very low tax bracket, the tax savings may be minimal. In taxable accounts, harvesting losses reduces your cost basis, which means potentially larger gains when you eventually sell the replacement investment. Also avoid harvesting losses just before a position is about to recover significantly. The strategy works best as part of ongoing portfolio management, not as a one-time event.

The Wash Sale Rule and Cross-Account Application

Section 1091 disallows a loss when 'substantially identical' securities are purchased within 30 days before or after the loss sale — a 61-day window total around the transaction. The disallowed loss is not lost forever: it adds to the basis of the replacement shares. But the taxpayer loses the current-year deduction, which is the entire point of harvesting in the first place. The rule applies across all accounts owned by the taxpayer and their spouse — including IRAs under Rev. Rul. 2008-5, which makes IRA repurchases permanently wash-saled (the basis step-up is lost forever inside the IRA).

What Counts as 'Substantially Identical'

• Same stock (AAPL for AAPL) — obviously substantially identical
• Same mutual fund in a different account — identical
• Different ETFs tracking the same index (VOO and IVV both S&P 500) — IRS has not ruled definitively; aggressive positions treat as non-identical, conservative positions treat as identical
• ETF vs mutual fund of same index provider (VOO vs VFIAX) — conservative treatment as identical
• Stock vs its own call option on the same underlying — substantially identical per Rev. Rul. 56-133
• Different share classes (BRK.A vs BRK.B) — not substantially identical per IRS practice

The $3,000 Ordinary Income Offset and Carryforward

Net capital losses first offset net capital gains dollar-for-dollar with no limit. Excess net losses offset up to $3,000 of ordinary income per year ($1,500 if MFS) under Section 1211(b). Any remaining loss carries forward indefinitely — long-term losses maintain long-term character, short-term maintain short-term. A $50,000 harvested loss with no realized gains produces $3,000 of ordinary-income offset this year and $47,000 carried forward — which, at $3,000 per year, would take 16 years to exhaust absent future gains. Harvesting losses in excess of foreseeable gains is rarely the highest-value use of tax-aware portfolio management.

References

• IRS: Topic 409 Capital Gains and Losses (irs.gov/taxtopics/tc409)
• IRS: Publication 550 Investment Income and Expenses (irs.gov/publications/p550)

Key Takeaways

• Realized capital losses offset realized capital gains dollar-for-dollar; up to $3,000 of net loss offsets ordinary income annually.
• Excess losses carry forward indefinitely and can offset future gains and $3,000/year of ordinary income.
• Wash sale rule: buying the same/substantially identical security within 30 days before or after the sale disallows the loss.
• Harvesting works best in December for annual loss matching, or throughout the year in volatile periods.
• Charitable giving of appreciated long-term holdings is the mirror strategy: avoid gain + get deduction.

Common Mistakes to Avoid

• Selling and rebuying the same ETF immediately, triggering wash sale and wasting the loss harvest.
• Accidentally triggering wash sale via IRA or 401(k) purchases of the same security.
• Harvesting in a tax-advantaged account — losses inside IRAs/401(k)s have no tax effect.
• Harvesting a short-term loss against a long-term gain, when the loss ordering rules pair them worst-first.
• Harvesting small losses that don't offset commissions or bid-ask spread impact.

Isla's December Harvest: $9,200 Losses Offset $11,400 Gains

Isla D. files jointly with her spouse in Pennsylvania with combined wages of $168,000. Her taxable brokerage account had both winners and losers in 2025: $11,400 of realized long-term gains earlier in the year, and unrealized losses in several mid-cap positions. A late-November tax-loss-harvesting exercise netted against the gains and saved her $1,380 of federal tax in a single afternoon of trades.

• Realized LTCG from earlier sales: +$11,400
• Unrealized losses identified in losing positions: −$9,200 (tech, small-cap, international)
• Wash-sale rule checked: replacement ETFs are not 'substantially identical' (VTI → ITOT swap, IEMG → SCHE swap)
• After harvesting: net realized gain reduced to $2,200
• Federal tax saved: $9,200 × 15% LTCG rate = $1,380
• Pennsylvania state tax saved: $9,200 × 3.07% = $282
• Excess losses carried forward (if realized losses had exceeded gains): up to $3,000 per year against ordinary income, unlimited carryforward

Tax-loss harvesting works because capital losses offset capital gains dollar-for-dollar, then up to $3,000/year of remaining losses can offset ordinary income, then the rest carries forward indefinitely. The wash-sale rule is the main trap: you cannot buy back the same security (or 'substantially identical' security) within 30 days before or after the sale. Switching from VTI to a different total-market ETF like ITOT is accepted; switching between two S&P 500 ETFs like VOO and SPY is generally not. Done correctly, harvesting adds an estimated 0.2–0.5% to long-run after-tax returns.

Scenario: Hendrix M. Harvests Losses in December

Hendrix M., single in Maine at $180,000, held $12,000 of unrealized losses and $8,000 of realized short-term gains in his taxable brokerage account by early December. Selling losers before year-end converts paper losses into real offsets - subject to the 30-day wash-sale rule (Section 1091).

• Short-term gains YTD: $8,000. Long-term gains YTD: $4,500.
• Sold losers: $12,000 realized losses (mix of short and long term). Netted against gains.
• Net capital result: minus $12,000 plus $12,500 = $500 small gain.
• Avoided tax (had losses not been harvested): $8,000 x 32% plus $4,500 x 15% = $3,235 of tax shifted or deferred.
• Replaced exposure: bought a similar-but-not-substantially-identical ETF to maintain market position.

Hendrix's end-of-year harvest eliminated roughly $3,235 of federal tax. If losses had exceeded gains, up to $3,000 of net loss deducts against ordinary income with the remainder carrying forward. Wash-sale rule voids the loss if the same or substantially identical security is purchased 30 days before or after the sale - in the same account, a spouse's account, or an IRA. Publication 550 covers every flavor of capital loss treatment.