What Is Tax Loss Harvesting, Anyway?

Most investors have heard the term, but almost none are doing it systematically. Tax loss harvesting sounds like it belongs in an accountant’s office – but the real value shows up in your portfolio, compounding quietly over decades. Here is how it actually works.

The Basic Idea

When a position in your portfolio drops below what you paid for it, you have an unrealized loss. Most investors ignore it, wait for the position to recover, and move on. That’s leaving money on the table.

Tax loss harvesting means you sell that position deliberately, lock in the loss on paper, and immediately reinvest in something similar – so your market exposure stays essentially the same. The loss you just realized can now be used to offset gains elsewhere in your portfolio, or up to $3,000 of ordinary income per year. Anything you don’t use this year carries forward indefinitely.

You haven’t changed your investment strategy. You haven’t permanently exited a position. You’ve just converted a paper loss into a tax asset – what I call a loss bank.

The Wash Sale Rule

There’s one rule you have to respect: the IRS wash sale rule. If you sell a position at a loss and buy the same or a “substantially identical” security within 30 days before or after the sale, the loss is disallowed. The workaround is straightforward – you buy something similar but not identical. Sell a broad S&P 500 ETF, buy a total market ETF. Same exposure, different fund, loss preserved.

This is where execution matters. Done sloppily, you trigger a wash sale and lose the benefit. Done correctly, it’s clean and repeatable.

Why Most Investors Never Do It

Three reasons. First, it requires active monitoring – you have to be watching for opportunities, not just checking your balance once a quarter. Second, most advisors manage at the account level, not the tax level – they’re not looking at your full picture when they make trades. Third, it feels counterintuitive. Nobody likes selling a losing position. It feels like admitting defeat. It isn’t.

The loss is already there. The question is whether you capture it or let it expire unused.

The Compounding Effect

Here’s what makes this genuinely powerful over time. The tax you defer by harvesting losses today stays invested. That capital keeps compounding. And when you eventually do pay the tax – because you will, eventually – you’ve had years of additional growth on money that would otherwise have gone to the IRS immediately.

Done systematically over a 20- or 30-year investment horizon, the after-tax difference between a portfolio that harvests losses and one that doesn’t can be substantial – often measured in hundreds of thousands of dollars on a seven-figure portfolio. Not from better stock picks or market timing, but from being more deliberate about taxes.

That’s the only free lunch left in investing. And most people are leaving it on the table.