Tax-Loss Harvesting — IRS Rules, Wash Sale Math, and Real ROI by Tax Bracket
Tax-loss harvesting adds 0.5-1.0% annually to taxable returns. The 30-day wash sale rule has nuances most articles miss. Here is the rule, ROI math, and when not worth doing.
Tax-loss harvesting (TLH) — selling investments at a loss to offset capital gains taxes — is the highest-leverage tax optimization available to taxable-account investors. Vanguard’s 2024 research shows well-executed TLH adds 0.45-1.05% annually in after-tax returns, with the average around 0.7%. On a $500,000 taxable account, that’s $3,500 of tax savings per year. Compounded over 20-30 years, the benefit can exceed $100,000 in lifetime tax-equivalent return.
The catch: the IRS wash sale rule (Section 1091) restricts how you can buy back into similar positions, and most popular TLH guides simplify the rule incorrectly. This article walks through the actual mechanics, the precise IRS language, when TLH is worth doing, and the common mistakes that turn the strategy into either zero benefit or an audit risk.
What TLH actually does
A taxable account holds an ETF (e.g., VTI) bought at $100/share. Two years later VTI is at $85 — a 15% paper loss. You haven’t realized the loss because you haven’t sold.
Tax-loss harvesting:
- Sell VTI at $85, locking in $15/share loss
- Immediately (or within seconds) buy a similar-but-not-identical ETF (e.g., ITOT — iShares Core S&P Total Market) at $85
- Your portfolio is still ~100% US stocks at the same price level
- You now have a $15/share realized capital loss to use against capital gains on your tax return
Year-end tax filing: the realized loss reduces your taxable capital gains dollar-for-dollar. If you have $5,000 of capital gains and harvested $5,000 of losses, your taxable capital gain is $0 — you save $750-1,200 in capital gains tax (depending on bracket and holding period).
The IRS wash sale rule precisely
IRS Publication 550 and Section 1091 of the tax code define the wash sale rule. The simple version most articles repeat: “Don’t buy back the same security within 30 days.” That’s incomplete and wrong in the details.
The precise rule:
A wash sale occurs when you sell a security at a loss and buy a substantially identical security within 30 days before or 30 days after the sale date. The disallowed loss is added to the cost basis of the replacement security, deferred until you eventually sell the replacement.
Three nuances most guides miss:
1. The 61-day window (not 30)
The window covers the 30 days BEFORE the sale plus 30 days AFTER plus the sale day itself = 61 days total. If you bought VTI 25 days before selling at a loss, that prior purchase triggers a wash sale even though you didn’t buy after the loss sale.
2. “Substantially identical” is a gradient
For individual stocks: identical CUSIP = wash. (Apple = Apple.)
For ETFs/mutual funds: the IRS hasn’t officially defined “substantially identical.” Common practice:
- VOO ↔ IVV (both S&P 500): probably wash (same index, near-identical holdings)
- VOO ↔ VTI (S&P 500 vs Total Market): not wash (different index)
- VTI ↔ ITOT (different providers, similar Total Market exposure): probably NOT wash
- VFIAX ↔ VOO (mutual fund + ETF version of same index): same fund, probably wash
The safest practice: swap to a different index family. S&P 500 → Total Market, Total Market → Russell 3000, US Large Cap → US Mid-Cap. The exposure is similar but the underlying index isn’t.
3. The wash sale applies across all your accounts
If you sell VTI at a loss in your taxable account and your spouse buys VTI in their account within 30 days, that’s a wash sale. If you buy VTI in your IRA within 30 days, that’s also a wash sale. The rule applies to all accounts you control or that file jointly with you.
The disallowed loss permanently disappears in the IRA case. Because IRAs don’t track cost basis the same way, the wash sale loss is forfeited rather than deferred. Avoid TLH if you’ll buy similar securities in any IRA within 30 days.
The realistic ROI math by tax bracket
Vanguard’s 2024 TLH research modeled the benefit across realistic scenarios. For a $500K taxable account, 70/30 stock/bond, with quarterly TLH execution:
| Federal bracket | State tax | Typical TLH benefit |
|---|---|---|
| 12% | 0% (TX, FL) | 0.05-0.15% |
| 22% | 5% | 0.30-0.50% |
| 24% | 0% | 0.40-0.60% |
| 24% | 9% (CA) | 0.65-0.85% |
| 32% | 9% (CA) | 0.80-1.00% |
| 37% | 12% (NYC) | 1.00-1.20% |
TLH is most valuable for high-bracket, high-tax-state residents. California, New York, and New Jersey investors in the top federal brackets see the largest benefit. Texas, Florida, Washington (no state income tax) at low federal brackets see minimal benefit.
The mechanism: TLH defers gains. Deferred gains compound at the pre-tax rate. The benefit is the time-value of taxes deferred. Higher tax rate → more taxes deferred → more compounding benefit.
The pairs that work for TLH
Common TLH pairs that are different enough to avoid wash sale concerns but similar enough to maintain exposure:
US large-cap stocks
- VOO (Vanguard S&P 500) ↔ IVV (iShares Core S&P 500) — risk: arguably substantially identical
- VOO ↔ VTI (Total Market) — safer, slight different exposure (adds mid-cap and small-cap)
- VOO ↔ ITOT (iShares Total Market) — different provider + index, low wash risk
US total market
- VTI ↔ SCHB (Schwab Broad Market) — different provider, same exposure
- VTI ↔ ITOT — different provider, similar exposure
International stocks
- VXUS (Vanguard Total International) ↔ IXUS (iShares Total International) — different provider, low wash risk
- VEA (Developed) ↔ SCHF (Schwab Developed) — different provider, low wash risk
US bonds
- BND (Vanguard Total Bond) ↔ AGG (iShares Total Bond) — different provider, low wash risk
- BND ↔ SCHZ (Schwab Total Bond) — different provider, low wash risk
Pre-build TLH pairs before you need them. Once you have a $500 loss and need to act, you don’t want to research substitutes.
When NOT to TLH
Three scenarios where TLH is worse than doing nothing:
1. You’re in a low tax bracket
12% federal bracket: long-term capital gains taxed at 0% federal. No tax to save. Stop here.
22% federal bracket with no state tax: long-term gains taxed at 15% federal only. The TLH benefit (~0.3% annually) is real but small relative to the operational complexity. Most 22% bracket investors should skip TLH unless they’re naturally low-effort about it.
2. You’re approaching retirement and will harvest gains soon
If you’ll sell most of your taxable account in 2-3 years (e.g., to fund retirement), the TLH benefit becomes complicated. You’re deferring losses that will offset gains you’ll realize anyway. The arithmetic still works but the operational complexity isn’t worth marginal benefit.
3. You don’t have realized capital gains
Capital losses offset capital gains first. After offsetting all gains, the next $3,000 of losses can offset ordinary income. Beyond that, losses carry forward indefinitely.
If you’re a buy-and-hold investor with no realized gains in a given year, you can only use $3,000 of losses against ordinary income. The rest carries forward — not lost, but delayed. TLH is more useful when you have regular realized gains (rebalancing, position trimming, end-of-year distributions).
Robo-advisor TLH — when it’s worth the fee
Wealthfront, Betterment, and Schwab Intelligent Portfolios offer automatic TLH. They monitor positions daily and execute when losses exceed thresholds.
| Service | Management fee | TLH effectiveness |
|---|---|---|
| Wealthfront | 0.25% | 0.6-0.9% TLH benefit (gross) |
| Betterment | 0.25% | 0.5-0.8% (gross) |
| Schwab Intelligent Portfolios | 0% | 0.4-0.7% (gross) |
| Vanguard PAS | 0.30% | Hybrid robo + advisor |
| DIY (zero fee) | 0% | 0.4-1.0% (with effort) |
Net of fees, robo TLH delivers 0.3-0.6% extra return for investors who otherwise wouldn’t TLH manually. For DIY-comfortable investors, manual TLH executing 2-4 trades per year captures most of the same benefit at zero cost.
The robo win case: investors with $200K+ taxable accounts in high tax brackets who don’t want to monitor and execute trades.
The practical TLH workflow
For DIY taxable account investors:
Quarterly review
End of each quarter (March 31, June 30, September 30, December 31): check positions for losses exceeding $500 per holding.
Execute the swap
If a position has a $500+ loss:
- Sell the losing position
- Immediately buy the pre-defined TLH pair (different index/provider)
- Record the sale + buy in your investment notes (date, amount, replacement)
- Set a calendar reminder for 31 days later — don’t repurchase the original until then
Year-end planning
In December:
- Tally realized losses harvested during the year
- Consider whether to harvest additional gains (if you have less than $3,000 in losses) to use the ordinary-income offset
- Plan the following year’s expected gains/losses
The bottom line
Tax-loss harvesting adds 0.5-1.0% to taxable account returns for high-bracket investors. The IRS wash sale rule is more nuanced than “don’t buy the same thing for 30 days” — the 61-day window includes both before and after the sale, and “substantially identical” is interpreted strictly.
For low-bracket investors or tax-advantaged accounts, TLH provides minimal benefit. For 24%+ federal bracket investors with significant state tax, TLH is worth doing — either DIY quarterly or via robo-advisor.
Pre-build your TLH pairs. Track wash sale windows carefully. Don’t TLH in IRAs. Don’t accidentally trigger wash sales by repurchasing in spouse’s accounts. Otherwise, the 0.7% annual tax alpha compounds to substantial wealth over decades.