Tax-loss harvesting is the practice of intentionally selling a losing position before year-end to realize the capital loss, then using that loss to offset realized capital gains and reduce taxable income. For active traders who accumulate short-term gains taxed as ordinary income — rates up to 37% — it is one of the few tax levers available after a trade is closed.
Key Takeaways
- Short-term gains are taxed as ordinary income (up to 37%), making harvesting far more valuable for active traders than for buy-and-hold investors who qualify for the 15–20% long-term rate.
- The IRS wash sale rule (IRC §1091) disallows a harvested loss if the same or substantially identical security is repurchased within 30 days on either side of the sale — including purchases in IRAs and other accounts.
- Losses must settle before December 31; for stocks (T+1 settlement), the practical sell deadline is approximately December 29–30.
How Tax-Loss Harvesting Works
The mechanics follow a simple sequence. First, identify positions with unrealized losses large enough to justify the trade. Second, sell the position to realize the loss. Third, apply that loss against realized gains on your tax return. Losses offset same-type gains first — short-term losses against short-term gains, long-term losses against long-term gains. Excess losses cross over to the other category, and any net loss remaining after offsetting all gains can reduce ordinary income by up to $3,000 per year, with unlimited carryforward under IRC §1212.
Two rates make harvesting especially powerful for active traders:
- Short-term capital gains (positions held under one year) are taxed at ordinary income brackets: 10%, 12%, 22%, 24%, 32%, 35%, or 37% depending on total income.
- Net Investment Income Tax (NIIT) adds a 3.8% surtax for taxpayers with MAGI above $200,000 (single) or $250,000 (married filing jointly), pushing the effective top rate to 40.8%.
By contrast, long-term gains are taxed at 0%, 15%, or 20%. A trader generating primarily short-term gains has nearly twice the tax incentive to harvest compared to a passive investor.
Practical Example
A trader closes November with $150,000 in short-term gains from ES futures and SPY options. Two open equity positions sit underwater: RIVN at an $18,000 unrealized loss and SOFI at a $9,000 unrealized loss.
Selling both before December 20 (settling before December 31) harvests $27,000 in losses:
Net short-term gains: $150,000 − $27,000 = $123,000
Tax saved: $27,000 × 40.8% (37% + 3.8% NIIT) ≈ $11,016
To avoid triggering the wash sale rule, the trader waits 31 days before rebuying RIVN. During the blackout period, they buy DRIV (a diversified EV ETF) to maintain sector exposure without repurchasing a substantially identical security. SOFI has no obvious substitute ETF, so they simply remain flat until the window closes.
The cost basis of any replacement position is unaffected — it is established fresh when purchased after the 30-day window.
Tax-loss harvesting means selling a losing position before year-end to capture the loss on your taxes. That loss offsets gains you’ve already realized, reducing what you owe. Active traders with short-term gains benefit most because those gains are taxed at the highest ordinary income rates.
Common Mistakes
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Triggering accidental wash sales across accounts. Active traders who trade the same ticker in a brokerage account and an IRA simultaneously are especially vulnerable. A loss sale in the taxable account is disallowed if the IRA buys the same security within the 61-day window — brokers do not flag cross-account wash sales automatically.
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Missing the settlement deadline. Stocks settle T+1. A sell order executed on December 31 settles in January of the next tax year, making the loss useless for the current year. Plan harvesting trades by December 29 at the latest.
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Ignoring the Section 475(f) election. Very active traders who qualify as traders in securities can elect mark-to-market accounting under Section 475(f). This converts gains and losses to ordinary income/loss, eliminates wash sale exposure entirely, and removes the $3,000 cap on loss deductions. The election must be filed by April 15 of the tax year it applies to — it cannot be made retroactively.
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Harvesting losses that reset a profitable thesis. If the position is losing only due to temporary volatility and the setup is still valid, locking in the loss may cost more in missed upside than it saves in taxes. Calculate the break-even recovery needed before harvesting.
How JournalPlus Tracks Tax-Loss Harvesting
JournalPlus displays realized P&L by position, date, and holding period, giving traders a running year-to-date view of their short-term and long-term gain/loss totals. The P&L export includes per-trade cost basis and proceeds, which maps directly to the data needed for Schedule D preparation. Traders approaching year-end can sort open positions by unrealized loss to quickly identify harvesting candidates before the settlement deadline.
