Tax-Loss Harvesting: Mostly a Deferral, Sometimes Real Money
Last updated August 2026
Short answer
Harvesting sells a position at a loss to offset gains, then buys something similar so you stay invested. The step almost nobody mentions is the fourth one: your cost basis is now lower, so the gain comes back when you eventually sell. Most of the benefit is therefore deferral rather than elimination. Deferral is still worth something, and four narrower effects are genuine savings. It is worth nothing at all inside an IRA or 401(k), which is where most people's money sits. Walnut is informational and is not an investment adviser.
This is the one robo-advisor feature that can plausibly pay for itself, which is why it appears in every pitch, usually with a percentage attached. It is also the most widely misdescribed, because the sentence that makes it honest, that the tax mostly comes back later, is not a good sentence for a marketing page.
The four steps, including the one that gets left out
1. A position falls below what you paid
The account holds a fund worth less than its purchase price. Nothing has happened for tax purposes yet, because an unrealised loss is not a loss the tax code recognises.
2. It is sold, which realises the loss
Now the loss exists on paper for tax purposes. It offsets realised capital gains first, and a limited amount of ordinary income beyond that, with anything left over carried into future years.
3. Something similar is bought immediately
The point is to stay invested, so the proceeds go into a fund tracking a related but not identical index. Being out of the market during a rebound would cost more than the tax saved.
4. Your cost basis is now lower
This is the step everyone skips. You own a similar position purchased at a lower price, so when you eventually sell, the gain is larger by roughly the amount you harvested. The tax did not vanish, it moved.
Step four is the whole reason this page exists. A harvest is not free money extracted from a falling market, it is a trade of tax today for tax later, and every honest estimate of its value has to account for the larger gain waiting at the other end.
Four ways it still produces real value
1. Deferral itself has value
Tax you pay in twenty years instead of this year leaves money invested and compounding in the meantime. Over long periods that is a genuine benefit, and it is the honest core of the case for harvesting.
2. Your bracket may be lower later
Harvesting deducts against income at today's rate and adds to gains taxed at a future rate. For someone whose income drops in retirement, that arbitrage is real money rather than timing.
3. The offset against ordinary income
Losses beyond your gains can offset a limited amount of ordinary income each year, which is taxed at a higher rate than long-term gains. That portion is a rate difference rather than a deferral, and it is the cleanest benefit available.
4. The basis may never be realised
Positions donated to charity or held until death can escape the embedded gain entirely under current rules. If that is your plan, the deferral becomes permanent, which is the strongest version of the argument and depends on rules that can change.
The third is the cleanest because it is a rate difference rather than a timing difference. Offsetting ordinary income, taxed at your marginal rate, against a future long-term gain taxed at a lower rate is an arbitrage that does not reverse.
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Three situations where it is worth nothing
| Situation | Why it does nothing |
|---|---|
| An IRA, 401(k) or any tax-advantaged account | Losses have no tax consequence there. This is the big one, and it covers most people's money |
| You have no gains and little taxable income | The offset needs something to offset. A low bracket makes the deduction worth little |
| A portfolio with nothing at a loss | After a long rise, there is frequently nothing to harvest, and the feature sits idle while the fee does not |
The first row deserves emphasis because of how much money it covers. Retirement accounts hold the majority of most households' investments, and inside them a loss has no tax effect whatsoever. Anyone whose portfolio is entirely in an IRA or an employer plan is paying for a feature that cannot operate. See robo-advisor versus target-date fund, where this decides the comparison.
Five things to watch
| Watch | Why |
|---|---|
| The wash-sale rule | Buying a substantially identical security within 30 days before or after disallows the loss |
| Your other accounts | A purchase in your IRA, or by a spouse, can trigger a wash sale against a sale in your taxable account |
| Automatic dividend reinvestment | A reinvested dividend is a purchase, and it can quietly disallow part of a harvest |
| Drift from your intended holdings | Repeated swapping into related funds can leave you holding second-choice products |
| The tax cost of ever leaving | A heavily harvested account has a low basis, so unwinding it later realises more gain |
The second is the trap that catches careful people. The wash-sale rule reaches across all your accounts, including an IRA and a spouse's accounts, so a scheduled purchase somewhere else can disallow a loss harvested in your taxable account. Automated systems can only avoid what they can see, which is an argument for connecting everything rather than for trusting the automation.
Related: do robo-advisors beat the market, and robo-advisors for tax-efficient investing.
FAQ
How does tax-loss harvesting work?
A position worth less than you paid is sold, which realises a loss that offsets realised gains and a limited amount of ordinary income. The proceeds immediately buy something similar so you stay invested. The step people miss is that your cost basis is now lower, so a larger gain arrives when you eventually sell.
Does tax-loss harvesting actually save money?
Mostly it defers tax rather than eliminating it, because the lower basis brings the gain back later. Deferral is still worth something, since the money stays invested in the meantime, and three narrower effects are real savings: a lower future bracket, the offset against ordinary income, and gains that are never realised.
Does tax-loss harvesting work in an IRA?
No. Losses inside an IRA, 401(k) or any tax-advantaged account have no tax consequence, so there is nothing to harvest. This matters because it is where most people's money sits, and it removes the single strongest argument for paying a robo-advisor fee.
What is the wash-sale rule?
If you buy a substantially identical security within 30 days before or after selling at a loss, the loss is disallowed for now and added to the basis of the new position. It applies across all your accounts including retirement accounts and a spouse's, which is why automated harvesting needs to know about accounts elsewhere.
How much can tax-loss harvesting save per year?
It depends on your bracket, your realised gains and how much fell in value that year, so no fixed figure applies. Estimates published by providers assume a high bracket and favourable market conditions, and the honest version is that in some years it is worth real money and in others it does nothing.
Can I do tax-loss harvesting myself?
Yes, and for a portfolio of a few funds it is not difficult: look for positions below their purchase price, sell, buy something similar and avoid repurchasing the same fund within the window. What automation adds is doing it continuously through the year rather than once in December, which is where much of the benefit is.
Is tax-loss harvesting worth the robo-advisor fee?
In a taxable account with a high bracket and gains to offset, it plausibly is, and it is the one robo feature that can exceed its cost. Four conditions have to hold at once, and if any fails, particularly the account type, the feature is switched off while the fee is not.
What is the downside?
A lower basis means a larger taxable gain whenever you sell, so a heavily harvested account is more expensive to unwind. Repeated swapping can also leave you holding second-choice funds, and a wash sale triggered by a purchase in another account can disallow the loss without you noticing.
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Walnut is informational and is not an investment adviser, and nothing here is investment advice or tax advice. Tax rules change and depend on your circumstances, so confirm anything here with a qualified tax professional before acting.