The IRS lets you deduct up to $3,000 in net capital losses against ordinary income every year. Any unused losses carry forward indefinitely until fully deducted. For an investor in the 24% federal + 5% state tax bracket, that's $870 in actual tax savings, every year, for doing a single trade. Over 30 years, that's $26,100 in tax savings — and yet most retail investors never claim the deduction.
The mechanics are simple enough that anyone with a brokerage account can execute them in 10 minutes. The complications are in the wash sale rule and position tracking, both of which are manageable once understood.
The Basic Mechanics
You own 100 shares of ABC stock at $80 cost basis. ABC is currently trading at $50. Unrealized loss: $3,000.
You sell the 100 shares. Realized loss: $3,000.
On your tax return: $3,000 deducted from ordinary income (or offset against capital gains). Tax savings at 24%/5% bracket: $870.
The next piece — the one most retail investors skip — is immediately buying a substitute investment that maintains your portfolio exposure. You can't rebuy ABC within 30 days (wash sale rule, details below), but you can buy something similar. For example, if ABC is a semiconductor stock, buy SOXX (iShares Semiconductor ETF) instead. Your sector exposure continues; only your tax basis changed.
The Wash Sale Rule
IRS rule: if you sell a security at a loss and buy the same or "substantially identical" security within 30 days before or after the sale, the loss is disallowed. The loss is added to the cost basis of the new purchase.
"Substantially identical" is the key phrase. The IRS has never definitively defined it. Common practice:
- Same ticker: clearly substantially identical (rule applies)
- Same index tracked by different funds: gray area, usually treated as substantially identical
- Different funds tracking different but similar indexes: safer ground
- Individual stocks in the same sector: clearly NOT substantially identical
The practical workarounds:
- VTI → ITOT (different providers, different underlying indexes): generally safe
- VOO → IVV → SPY: all three track S&P 500, gray area — some advisors consider them substantially identical
- SCHD → DGRO: different methodologies, clearly not substantially identical
- Apple → Microsoft: completely different companies, no issue
Common practice in the industry: VTI → ITOT is considered safe because they track different indexes (CRSP vs. S&P Total Market). Some purists argue this is aggressive. In practice, the IRS has never successfully enforced wash sale rules on different-index funds, though they theoretically could.
The Matched Pair Strategy
Professional wealth managers use "matched pairs" for systematic tax-loss harvesting:
- VTI ↔ ITOT (total US market)
- VOO ↔ IVV (S&P 500 — aggressive)
- VXUS ↔ IXUS (total international)
- SCHD ↔ VYM (dividend)
- BND ↔ AGG (total bond)
When one is at a loss, sell it and buy the pair. Wait 31 days. Then consider flipping back if advantageous. This maintains continuous market exposure while harvesting losses.
The Annual Limit and Carryforward
The $3,000 annual deduction applies to net losses (after offsetting any realized gains). Calculation:
- Total capital gains - total capital losses = net capital gain/loss
- If net loss: deduct up to $3,000 from ordinary income this year
- Any excess losses carry forward to next year
Example: You realized $8,000 in losses and $2,000 in gains in 2026. Net loss: $6,000. Deduct $3,000 against ordinary income. Carry forward $3,000 to 2027.
Carryforwards don't expire. Some retirees have losses from the 2008 bear market that still reduce their tax bills 15+ years later. Losses are a permanent tax asset.
When to Harvest
The optimal trigger is relative, not absolute. Don't wait for losses to be huge. Don't harvest for tiny losses (the transaction cost and complexity aren't worth it).
Rules of thumb:
- Position is down 10%+ and amount represents meaningful dollars (say, $2,000+)
- You have a clean substitute to buy
- You don't need to sell for liquidity reasons
Harvest opportunistically. Don't wait for December — that's when everyone else is harvesting, and substitutes may be less liquid. A March harvest during a temporary market dip can be better than a forced December harvest.
The Cost Basis Method Decision
Most brokerages default to "average cost" for mutual funds and "FIFO" (first in, first out) for individual stocks. Neither is optimal for tax-loss harvesting.
Best method for harvesting: "Specific Identification" (SpecID). You tell the brokerage exactly which lots to sell, choosing the ones with the highest cost basis (biggest losses).
At Fidelity/Schwab: change your account-default method to SpecID. Or, when placing sell orders, manually specify the tax lot. This lets you harvest only the losing portion of a holding while preserving the gains.
Example: you own 1,000 shares of VTI bought in three lots:
- 300 shares at $200 (currently $180 = $6,000 loss)
- 400 shares at $220 (currently $180 = $16,000 loss)
- 300 shares at $150 (currently $180 = $9,000 gain)
With SpecID, you can sell only the 400 shares at $220 cost basis to harvest a $16,000 loss, leaving the gain untouched. With FIFO, you'd sell the oldest lot first (different result). With average cost, you can't cherry-pick at all.
The Bracket Strategy
Tax-loss harvesting is more valuable in higher brackets. At 37% federal + 13.3% California = 50.3% marginal rate, a $3,000 deduction is worth $1,509 in tax savings. At 12% federal + 0% Texas = 12% marginal, the same $3,000 saves $360.
If you're in a low bracket this year but expect higher in future years, consider not harvesting — preserve the loss for a higher-bracket year.
Conversely, if you're in a high bracket now but expect retirement to lower your bracket, harvest aggressively now. The tax savings compound.
Coordinating with Realized Gains
Losses are most valuable when they offset short-term capital gains (taxed at ordinary income rates, up to 37%). They're less valuable against long-term gains (taxed at 0%, 15%, or 20%).
If you have short-term gains to offset, prioritize harvesting. If you only have long-term gains or no gains, still harvest against ordinary income — but understand the tax savings are smaller.
The Robo-Advisor Automation
Wealthfront and Betterment offer automated tax-loss harvesting. They scan your taxable accounts daily and execute harvests whenever opportunities arise. The quoted benefit is 0.5-1.0% in "tax alpha" — effectively an improvement in after-tax returns.
For DIY investors, you can replicate 80% of this benefit with quarterly manual review. Check your taxable positions each quarter for unrealized losses over $2,000. Execute harvests when they exist. This takes 20 minutes per year.
For a $500,000 taxable portfolio, quarterly harvesting probably captures $5,000-$10,000 per year in realized losses that wouldn't otherwise be realized. Tax savings at 25% combined rate: $1,250-$2,500 per year. Over 30 years, substantially more than the robo-advisor's 0.25% fee would have cost.
The Year-End Cleanup
In December, review all taxable positions:
- Identify all positions currently at a loss
- Estimate realized gains for the year (from any sales or mutual fund distributions)
- Calculate how many losses you need to offset gains + $3,000 ordinary deduction
- Execute losses in amounts that achieve that total
- Buy substitute investments for each loss sold
Don't just harvest all losses. Harvest enough to maximize the current-year deduction. Excess losses carry forward and can be harvested in future years at potentially higher tax brackets.
The Pitfalls
- Wash sale violation: rebuying same security in another account (IRA, spouse's account) within 30 days still triggers the rule. Most retail investors are surprised to learn this.
- Forgetting to update mutual fund reinvestments: DRIP reinvestment into a sold fund within 30 days counts as a wash sale.
- Not tracking carryforwards: if you change tax software or preparers, manually verify your carryforward losses transfer.
- Harvesting in retirement accounts: doesn't work. Losses inside IRAs aren't deductible. Only taxable account losses qualify.
The Lifetime Value
Systematic tax-loss harvesting, executed 2-4 times per year in a taxable brokerage of $200K+, adds roughly 0.5-1.0% to annualized after-tax returns. Over 30 years on a $500K portfolio, that's $75,000-$150,000 in added wealth.
The required time investment: maybe 3-5 hours per year. No other retail investor strategy has this kind of return-to-effort ratio. It's the ultimate boring win.