Tax Loss Harvesting: The December Move That Millionaires Make Every Year

Tax loss harvesting turns a losing investment into an immediate tax break, and it’s one of the few strategies in investing that actually gets more useful when the market drops. Instead of just watching a position sit at a loss, you sell it, lock in that loss for tax purposes, and use it to offset gains elsewhere, or even a chunk of your ordinary income.

This isn’t a loophole. It’s a deliberate part of the tax code, and wealthy investors and their accountants use it every single December. There’s no reason an everyday investor with a taxable brokerage account can’t use the exact same move.

How Tax Loss Harvesting Works, Step by Step

1. You own a position in a taxable brokerage account that’s currently worth less than what you paid for it.
2. You sell that position, which “realizes” the loss for tax purposes.
3. You use the proceeds to buy a similar, but not identical, investment, so your money stays invested in the market.
4. Come tax time, that realized loss offsets capital gains from other investments you sold at a profit.
5. If your losses exceed your gains, up to $3,000 of the excess can offset ordinary income each year, with anything beyond that carried forward to future years indefinitely.

A Real Example of Tax Loss Harvesting

Say you bought $20,000 of an individual stock that’s now worth $15,000, a $5,000 loss. You also sold a different investment this year for a $4,000 gain. Without tax loss harvesting, you’d owe capital gains tax on that full $4,000. By harvesting the $5,000 loss, you wipe out the entire $4,000 gain and still have $1,000 left over to apply against your ordinary income, cutting your tax bill from a bad year into an unexpected small win.

The Wash Sale Rule: The One Thing That Trips People Up

The IRS wash sale rule says you can’t claim a tax loss if you buy the same, or a “substantially identical,” investment within 30 days before or after the sale. Buy back the exact same stock you just sold three days later, and the IRS disallows the loss entirely.

This is why step three in the process above matters so much. Instead of buying back the same fund, you swap into something similar, a different S&P 500 index fund from another provider, for example, so your portfolio stays roughly the same while staying clear of the wash sale rule. After 30 days pass, you’re free to swap back if you want to.

When Should You Harvest Losses?

December gets most of the attention because it’s the last chance to realize losses before the tax year closes, but tax loss harvesting can technically happen any time the market gives you a losing position to work with. Some robo-advisors, including Wealthfront and Betterment, automate this process year-round on taxable accounts, harvesting losses the moment they appear rather than waiting for a year-end scramble.

Where Tax Loss Harvesting Does (and Doesn’t) Apply

• Applies to: taxable brokerage accounts only.
• Does not apply to: Roth IRAs, traditional IRAs, or 401ks, since those accounts don’t generate taxable gains or losses in the first place.
• Works best for: investors with individual stocks or sector-specific ETFs, which see more price volatility and more frequent harvesting opportunities than a broad total-market fund.

Mistakes That Cost People Their Tax Loss Harvesting Benefit

The most common mistake is triggering an accidental wash sale by buying back a near-identical fund too soon, or by having a dividend reinvestment plan automatically repurchase shares of the same fund inside the 30-day window without realizing it. Turn off automatic reinvestment on any position you’re planning to harvest before you sell it.

The second mistake is harvesting losses on a long-term investment you actually believe in, just to chase a tax break, then never buying back in. Tax loss harvesting should adjust your tax bill, not your long-term investment strategy.

Tax Loss Harvesting: Frequently Asked Questions

How much can I deduct with tax loss harvesting?
Losses first offset capital gains dollar for dollar, with no limit. Any leftover loss can offset up to $3,000 of ordinary income per year, and unused losses beyond that carry forward to future tax years.

Does tax loss harvesting work in a Roth IRA?
No. Roth IRAs, traditional IRAs, and 401ks aren’t subject to capital gains tax in the same way, so there’s no tax loss to harvest inside those accounts.

Is tax loss harvesting worth doing for a small account?
It can still help, but the benefit scales with your account size and tax bracket. For very small taxable balances, the time and complexity may outweigh the tax savings, which is where an automated robo-advisor feature can do the work for you at no extra effort.

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