Selling Losers Before Year-End? How Tax-Loss Harvesting and the Wash-Sale Rule Actually Work

By late September, most investors can see which holdings in their taxable accounts are sitting at a loss. That raises a perennial fourth-quarter question: should you sell them before December 31 to lower this year's tax bill? The answer depends on your own gains, bracket, and holdings — but the mechanics are the same for everyone, and they are worth understanding before you act.

This article is educational and general. It is not tax advice for your situation; confirm the specifics with a qualified tax professional.

What does a realized loss actually do for you?

Selling an investment for less than you paid creates a capital loss. Losses are first netted against capital gains — short-term losses against short-term gains, long-term against long-term, and then across the two categories. If you end up with a net loss for the year, the IRS allows you to deduct up to $3,000 ($1,500 if married filing separately) against ordinary income such as wages, pension payments, or IRA withdrawals. Anything beyond that carries forward to future years, with no expiration, until it is used up.

Two things follow. First, a loss is most valuable when you have gains to absorb it — including the capital gain distributions mutual funds pay out in November and December. Second, harvesting doesn't make the money back. Because the replacement investment starts with a lower cost basis, much of the benefit is a deferral of tax rather than a permanent reduction; whether that is worth it depends on the rate you would pay now versus later.

What is the wash-sale rule?

This is where most mistakes happen. Under the wash-sale rule (IRS Publication 550), if you sell a security at a loss and buy a "substantially identical" security within 30 days before or 30 days after the sale — a 61-day window in total — the loss is disallowed for that year. The disallowed amount is added to the cost basis of the replacement shares, so it isn't lost forever, but it is pushed out until you eventually sell the replacement.

Some details that catch people:

• The window runs both directions. Buying shares three weeks before you sell at a loss triggers the rule just as surely as buying them after.
• Dividend reinvestment counts. An automatic reinvestment inside the window is a purchase.
• Your IRA counts too. In Revenue Ruling 2008-5, the IRS held that buying the substantially identical security in your traditional or Roth IRA within the window disallows the loss — and in that case the basis is not added to the IRA, so the loss is permanently forfeited rather than deferred.
• A spouse's accounts are generally treated the same way under the IRS's guidance on wash sales, so household coordination matters.
• "Substantially identical" is a judgment call. The same stock, or the same fund from a different account, clearly qualifies. Two different broad-market funds that track different indexes are generally treated as not substantially identical, but the IRS has not published a bright-line test; a tax professional should weigh in on close cases.

What happens with mutual funds in December?

A fourth-quarter trap: if you buy a replacement fund shortly before its year-end distribution, you may receive a taxable capital gain distribution on shares held for only days. The fund's price drops by the same amount, so you pay tax on money you effectively got back as a lower share price. Check a replacement fund's estimated distribution date before buying.

How does New York treat capital losses?

New York State follows the federal rules for calculating capital gains and losses, so the $3,000 limit and the carryforward apply on your state return as well. Keep in mind that New York taxes gains as ordinary income with no preferential long-term rate — we cover this in our New York capital gains guide — which means offsetting a gain with a loss can be worth somewhat more to a New York resident than the federal math alone suggests.

When is harvesting worth doing?

There is no universal answer. It tends to matter more when you have realized gains or expect fund distributions this year, when your bracket is higher now than you expect it to be later, and when a suitable replacement keeps your portfolio's risk profile intact. It can matter little — or backfire — if your gains would fall in the 0% long-term rate anyway, or if selling leaves you out of the market during a period you wanted exposure.

The bottom line

Tax-loss harvesting is an IRS-recognized way to manage the timing of taxes on a taxable portfolio. Its value is limited by your gains, capped at $3,000 of ordinary income per year beyond that, and easily undone by a repurchase within 61 days — including inside an IRA. Before selling, review every account in the household, check replacement funds' distribution dates, and have a tax professional confirm the result fits your year-end tax picture.

<!-- COMPLIANCE CHECKLIST before changing status to "published": [x] General/educational — no return promises, no specific security recommendations [x] Any figures cited are sourced and linked (IRS preferred) [x] Reviewed through your compliance process / CCO (approved 2026-09-21) [x] Title, description, tags filled in above; date to be set to next free Mon/Wed on approval [x] status changed from "draft" to "published" -->