Why Late October Beats December 31 for Tax-Loss Harvesting

Late December has its own routine. Investors scroll past red numbers between holiday errands, send off sell orders, and buy whatever replacement fund comes to mind first. The tax code punishes that hurry. Buy back the wrong thing within 30 days and you lose the deduction. Sell in the last days of the year and the wash sale window runs well into January.

Tax-loss harvesting works better as a fall review. If you start in late October, you have time to add up the year’s gains, pick a replacement without rushing, and let the wash sale window close before December 31.

The market gives you a reason to look early. The CBOE Volatility Index closed at 18.39 on October 26, 2026, up 23.7% from a month earlier. Choppier markets can leave more holdings worth less than you paid for them.

How a Harvested Loss Shrinks Your Capital Gains Bill

When you sell a position for less than you paid, the loss offsets capital gains you’ve already taken. If your losses are bigger than your gains, the IRS lets you deduct up to $3,000 ($1,500 if you are married and file a separate return) from ordinary income, such as IRA withdrawals or pension checks.

Whatever is left carries forward from year to year until it’s used up. A carried loss remains long-term or short-term, according to the 2025 edition of IRS Publication 550.

Here’s an example. A retired couple files jointly for 2026, and their taxable income falls in the 22% bracket, which starts at $100,800 for married couples filing jointly. Earlier in the year they took $15,000 in short-term gains, which are taxed at ordinary rates. They also own a fund that’s $22,000 below its cost basis.

Medicare enrollees get one more benefit. Gains raise modified adjusted gross income, and IRMAA surcharges kick in at set income tiers. On the 2026 schedule, a joint return above $218,000 increases each spouse’s Part B premium from $202.90 to $284.10 a month. Medicare sets premiums from income two years earlier, so a 2026 gain shows up on a 2028 bill.

October Sales Clear the Wash Sale Window Before December 31

Publication 550 describes a wash sale as selling stock or securities at a loss and, within 30 days before or after that sale, buying substantially identical stock or securities or an option to buy them. Buying them in your IRA or Roth IRA counts too. So does a purchase by your spouse.

In most wash sales, the disallowed loss gets added to the cost basis of the new shares, so you get the deduction later instead of now. A purchase inside an IRA is excluded from that basis adjustment. That loss can disappear for good.

The year-end rollover is where people get caught. In one Publication 550 example, shares sold on December 27, 2024 were followed by identical shares bought on January 10, 2025, and the loss was disallowed. Selling in late October closes the 30-day window by the end of November. That leaves December free to rebalance, buy back the original holding if you still want it, and review the whole year.

A Fall Checklist for Tax-Loss Harvesting

1. Add up your realized gains. Pull your brokerage’s realized gain and loss report for the year so far.
2. List every lot below cost basis. Shares bought at different times often have very different cost bases.
3. Check holding periods. For exchange-traded securities, the holding period begins the day after the trade date you bought. Anything held more than one year counts as long-term.
4. Pick a replacement that isn’t substantially identical. A fund that follows a different index or a different part of the market keeps you invested without triggering the wash sale rule.
5. Confirm the trade date. In Publication 550’s example, a stock sold on December 31, 2025 that settled in January belonged on the 2025 return. The trade date controls the tax year, not the settlement date.
6. Stop automatic purchases. Dividend reinvestment, your spouse’s account, and IRA contributions can all trigger a wash sale.

When Tax-Loss Harvesting Costs More Than It Saves

• Tax-deferred accounts don’t count. Selling at a loss inside an IRA or 401(k) gives you no deductible capital loss.
• Lower brackets get smaller savings. In the 12% bracket, the $3,000 deduction is worth about $360. If your long-term gains already fall in the 0% bracket, offsetting them saves nothing. The replacement shares also start with a lower cost basis, which means a bigger taxable gain when you eventually sell.
• Your allocation still matters. A $660 deduction isn’t worth selling an asset you want to own or leaving your portfolio unbalanced for a month.

Set aside an afternoon in the fall, pull the reports, and make your trades while December is still open. A late-October review leaves you time to correct mistakes before December 31. A rushed review in the last week of December doesn’t. The wash sale rule is only one of several IRS rules that quietly cost retirees real money; we covered nine of them in a free guide to the traps worth knowing before you file.

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