Tax-loss harvesting gets mentioned a lot as a year-end planning tactic, but it's often described in a way that makes it sound more powerful — or simpler — than it really is. Here's what it actually does, how the mechanics work, and when it's worth paying attention to.
What it is
Tax-loss harvesting is the practice of selling an investment at a loss in a taxable brokerage account in order to offset capital gains realized elsewhere in your portfolio. If your losses are larger than your gains, you can also use up to $3,000 of the excess ($1,500 if married filing separately) to offset ordinary income each year. Anything beyond that doesn't disappear — it carries forward indefinitely to future tax years until it's used up.
The netting happens in a specific order: short-term losses offset short-term gains first, long-term losses offset long-term gains first, and only after that do the two categories offset each other. This matters because short-term gains are taxed at ordinary income rates, so short-term losses are generally the more valuable ones to harvest.
The wash-sale rule
The IRS won't let you sell an investment at a loss and then simply buy it right back to preserve your position. Under the wash-sale rule, if you repurchase the same security — or one the IRS considers "substantially identical" — within 30 days before or after the sale (a 61-day window in total), the loss is disallowed for that tax year. It isn't lost forever; it gets added to the cost basis of the replacement shares, so you'll benefit from it eventually when those shares are sold. But it won't help you this year.
A few details that trip people up:
- The rule applies across all of your accounts - including a spouse's accounts and IRAs - not just the account where the sale happened.
- Replacing a fund with a near-identical one (e.g., swapping one S&P 500 index fund for another) can still trigger the rule if the IRS views them as substantially identical.
- Brokers report wash sales per account, so anyone with holdings spread across multiple institutions has to track this manually or with software - it doesn't happen automatically.
When it actually moves the needle
Tax-loss harvesting isn't a strategy that benefits every investor equally. A few things determine whether it's worth the attention:
It only applies to taxable accounts. Losses inside a 401(k) or IRA have no tax consequence, so there's nothing to harvest there.
It matters more at higher income and tax brackets. The value of an offset scales with your marginal rate — a loss is worth more to someone in the top bracket than to someone in a lower one. For high earners, harvested losses can also help reduce exposure to the 3.8% Net Investment Income Tax on investment income above certain thresholds.
Volatile years create more opportunity. You need positions trading below their purchase price to harvest a loss, so periods of market volatility — even within a portfolio that's up for the year overall — tend to create more candidates for harvesting than steady, straight-up markets.
It shouldn't drive the investment decision. The most common misstep is letting the tax benefit lead — selling a position purely to capture a loss and drifting away from a portfolio's target allocation, or parking the proceeds in something you don't actually want to hold for 31 days just to avoid a wash sale. The tax benefit should support the existing investment plan, not override it.
A simple example
Say an investor has a $10,000 realized gain from selling one position this year, and a separate holding sitting at a $4,000 loss. Selling the losing position brings the net taxable gain down to $6,000. If the investor also had a $15,000 loss instead, the full $10,000 gain would be offset, with $3,000 more applied against ordinary income — and the remaining $2,000 carried forward to next year.
Where it fits in a broader plan
Tax-loss harvesting works best as an ongoing, disciplined part of portfolio management rather than a once-a-year scramble in December. It also intersects with other decisions — Roth conversions, charitable giving, timing of a business sale — where realized losses can offset income created elsewhere in the same tax year. That coordination is usually where the real value shows up, more than the mechanical act of selling a losing position on its own.
This article is for general educational purposes and isn't intended as tax or legal advice. Tax-loss harvesting involves rules and exceptions specific to your situation - talk with your tax professional and financial advisor before acting on any of the strategies described here.
Sources
- IRS, Topic no. 409, Capital gains and losses
- Vanguard, Tax-loss harvesting explained
- Becker, Understanding Tax Loss Harvesting Rules
- H&R Block, What Is the Wash Sale Rule and Impact on Taxes
- Prudential Financial, Key Tax Impacts of the Wash-Sale Rule