Tax-Loss Harvesting: Use Your Losers to Cut Your Tax Bill

The basic concept

Tax-loss harvesting is the practice of selling investments that have declined in value to realize a loss for tax purposes. That realized loss then offsets realized capital gains elsewhere in your portfolio, reducing or eliminating the tax you owe on those gains.

If your losses exceed your gains, up to $3,000 of the excess offsets ordinary income each year. Any remaining losses carry forward indefinitely to future tax years.

The key insight: you do not have to leave the market to harvest a loss. You sell a position and immediately buy a similar but not “substantially identical” security, maintaining your market exposure while capturing the tax benefit.

How realized losses offset taxes

Capital gains and losses net against each other in a specific order. Short-term losses (assets held one year or less) offset short-term gains first, then long-term gains. Long-term losses (assets held more than one year) offset long-term gains first, then short-term gains.

This ordering matters because short-term gains are taxed as ordinary income (up to 37% for high earners), while long-term gains are taxed at 0%, 15%, or 20% depending on your income. Offsetting short-term gains is generally more valuable per dollar of loss than offsetting long-term gains.

The wash sale rule

The wash sale rule is the primary constraint. If you sell a security at a loss and buy the same or a “substantially identical” security within 30 days before or after the sale, the IRS disallows the loss. The disallowed loss is added to your cost basis in the new shares, deferring rather than eliminating the benefit.

“Substantially identical” is somewhat vague in the tax code, but generally covers the same stock, the same fund, or a fund tracking the same index from the same provider. Wash sale rules apply across all accounts you and your spouse control, including IRAs.

Loss carryforwards: the tax reserve

Unused capital losses do not expire. If you harvest $50,000 in losses and only have $20,000 in gains, the remaining $27,000 (after the $3,000 ordinary income offset) carries forward to future years. When you realize gains later, whether from rebalancing, a concentrated position sale, or any other event, those carry-forward losses are waiting to offset them.

Investors who harvest systematically over many years can build significant loss carry-forward balances that function like a tax reserve, absorbing future gains at no additional cost.

The ETF substitution approach

A clean way to harvest without leaving the market: sell an ETF at a loss and immediately buy a similar ETF that tracks a comparable but not identical index. Common pairings used by investors:

• VTI (Vanguard Total Stock Market) sold, ITOT (iShares Core Total US Market) purchased. Both cover the total US equity market but follow different indexes from different providers.
• EFA (iShares MSCI EAFE, developed international markets) sold, VEA (Vanguard FTSE Developed Markets) purchased. Similar exposure, not identical index.

Note: selling IVV and buying VOO (both tracking the S&P 500) is a wash sale risk since they follow the same index. Get guidance from your advisor before making specific substitutions.

Harvest throughout the year, not just in December

Most investors think about tax-loss harvesting in December when brokerage statements show year-to-date losses. By then, markets may have recovered and opportunities have passed.

Losses happen throughout the year, after corrections, sector selloffs, or individual earnings misses. A quarterly review of your portfolio for harvesting opportunities is more effective than a December scramble.

Common mistakes

• Triggering a wash sale by buying back the same security within 30 days. Track purchases carefully across all accounts.
• Harvesting without understanding cost basis. Realizing a loss resets your basis lower in the replacement security, creating larger future gains when you eventually sell. The strategy defers taxes, not eliminates them.
• Changing your investment exposure as part of the harvest. The goal is to capture the tax benefit without meaningfully changing your market positioning.
• Waiting until December. By then, many opportunities have closed. Monitor your portfolio periodically throughout the year.

This article is for educational purposes only and does not constitute tax, legal, or financial advice. Consult a licensed CPA, tax attorney, or enrolled agent before implementing any strategy. Tax laws change and your specific circumstances matter.