Tax-Loss Harvesting Explained: How It Works, the Wash-Sale Rule, and the Real Math

1. What Tax-Loss Harvesting Actually Does

Three things happen mechanically when you harvest a loss:

1. You sell a security that's currently below your purchase price, realizing the capital loss.
2. You buy a similar but not substantially identical security with the proceeds, maintaining your market exposure.
3. The realized loss reduces your taxable income — first offsetting capital gains, then up to $3,000 of ordinary income, with the remainder carrying forward to future tax years.

The strategy is only available in taxable brokerage accounts. Inside 401(k)s, IRAs, Roth IRAs, and HSAs, the tax wrapper makes individual gains and losses irrelevant.

2. A Concrete Example: $10,000 Loss, $2,400 Saved

You hold $100,000 of VTI (Vanguard Total Stock Market ETF) in a taxable brokerage account, bought at $250/share. The market drops 10% — VTI is now $225, and your position is worth $90,000. You have an unrealized loss of $10,000.

Without TLH: you do nothing. The loss exists on paper but provides no tax benefit. When VTI eventually recovers to $260, you'll have an unrealized gain of $4,000 — and someday a tax bill on it.

With TLH:

1. Sell all VTI for $90,000, realizing a $10,000 long-term capital loss.
2. Immediately buy $90,000 of ITOT (iShares Core S&P Total US Stock — different index, different provider). Your market exposure is essentially the same.
3. At year-end, your $10,000 loss offsets $10,000 of capital gains (or up to $3,000 of ordinary income).

Tax saving at a 24% marginal bracket: $10,000 × 24% = $2,400. That's real money returned to you — even though your investment thesis didn't change.

3. The Wash-Sale Rule (the Big Trap)

IRS Section 1091: if you buy a "substantially identical" security within 30 days before or 30 days after a sale at a loss, the IRS disallows the loss. The 61-day window catches most beginners.

What gets disallowed:

• Sell VTI on November 1, buy VTI on November 25 → loss disallowed.
• Sell VTI on November 1, your spouse buys VTI on November 15 → loss disallowed.
• Sell VTI in your taxable account, buy VTI in your IRA same day → loss disallowed AND no basis adjustment to recover later. This is the worst-case scenario — you lose the deduction and the basis is permanently gone.
• Sell VTI on October 5, dividend reinvestment plan (DRIP) automatically buys VTI on October 15 → wash sale on the small DRIP amount.

The rule applies across accounts, including spouse's accounts and IRAs. Turn off automatic dividend reinvestment in the security you're harvesting, or you'll trigger small wash sales on subsequent dividends.

When wash-sale is triggered: the disallowed loss is added to the cost basis of the replacement shares. So you don't lose the deduction permanently — it's just deferred until you sell those replacement shares (and those replacement shares haven't triggered another wash sale).

4. What "Substantially Identical" Means in Practice

The IRS has never published a formal test. The consensus from tax professionals:

The safest TLH pairs swap between different indexes (S&P 500 ↔ Total Market). Swapping between two ETFs that track the exact same index (VOO ↔ IVV) is in a gray zone the IRS has never explicitly tested but most advisors avoid.

5. The $3,000 Ordinary Income Offset and Carryforward

Capital losses are processed in this order:

1. Same-type netting: short-term losses offset short-term gains; long-term losses offset long-term gains.
2. Cross-type netting: any remaining loss offsets the opposite-type gain.
3. Ordinary income: up to $3,000 of remaining loss reduces ordinary income (W-2 wages, freelance income).
4. Carryforward: anything beyond $3,000 carries forward indefinitely to future tax years.

Example: you harvest $25,000 of long-term losses in 2026. You have $5,000 of long-term gains and $4,000 of short-term gains.

• $5,000 of LT loss offsets $5,000 of LT gains → net zero
• $4,000 of LT loss offsets $4,000 of ST gains (cross-type) → net zero
• $3,000 reduces ordinary income
• $13,000 carries forward to 2027 and beyond

The carryforward never expires. A $50,000 loss bank from a 2026 bear market can offset gains in 2030, 2035, or any future year — until your spouse passes away (filing status changes the carryforward rules).

6. When TLH Is Worth Doing — and When It Is Not

TLH is worth doing when:

• You have a taxable brokerage account. The strategy doesn't apply to retirement accounts.
• You hold appreciable losses — at least a few thousand dollars worth. Harvesting $200 isn't worth the trade friction.
• You're in a high tax bracket today and might be in a lower one later. The deferral is most valuable when today's rate is higher than the future rate.
• You have realized gains to offset. Recently sold property, stock options vesting, RSUs.

TLH is NOT worth doing when:

• You're in the 0% long-term capital gains bracket (single income under ~$48,000, married under ~$96,000). You owe no tax on long-term gains anyway, so deferring loses you nothing — and reduces your future basis.
• The position is small — bid-ask spread and trading friction outweigh the deduction.
• You're close to selling for a major life event (down payment, retirement). Harvesting reduces basis, increasing the eventual gain.

7. Robo-Advisor TLH vs Manual

Wealthfront, Betterment, and Schwab Intelligent Portfolios offer automated daily tax-loss harvesting. The robo monitors all your holdings every day, harvesting losses whenever it finds them and swapping into pre-defined replacement securities to avoid wash sales.

Wealthfront publishes data showing their TLH adds 1-2% in after-tax returns annually for high-bracket clients. The fee is 0.25% — so net benefit is 0.75-1.75% per year. On portfolios under $100,000, manual harvesting captures most of the benefit at zero cost. Above $250,000 in a high tax bracket, robo TLH can pay for itself many times over.

8. Step-by-Step: How to Harvest a Loss

For a typical DIY investor at Vanguard, Fidelity, or Schwab:

1. Identify a losing position in your taxable account — current value below cost basis.
2. Confirm no wash-sale risk: you haven't bought the same security in the past 30 days, and won't in the next 30. Turn off DRIP if it's on for that security.
3. Pick a replacement security. Different index, different provider. Sample swaps: VTI ↔ ITOT, VOO ↔ SCHX, VXUS ↔ IXUS, BND ↔ AGG.
4. Sell the losing position. Specify lots if your brokerage allows it — harvest the highest-cost-basis lots first to maximize the loss.
5. Immediately buy the replacement with the proceeds. Same dollar amount; same trading day if possible to minimize market drift.
6. Document the basis adjustment. The new replacement shares have basis equal to your purchase price (not the original basis from the harvested position).
7. Wait at least 31 days before swapping back — or just hold the replacement permanently.

Most major brokerages now have "tax-loss harvest" tools that surface eligible positions automatically and prevent wash-sale violations. Worth using even if you're harvesting manually.

Frequently Asked Questions