Tax-Loss Harvesting Value Calculator — Rex's Toolbox

Rex says

Money math without the spreadsheet headache. Plug in your numbers and I'll show you exactly where the dollars land.

Try a scenario

Click to load — tweak from there.

Inputs

Realized capital loss($)

Capital gains elsewhere this year($)

Rate on those gains (short or long-term)(%)

Marginal ordinary income rate(%)

Years you'll keep the tax savings invested

Expected return on reinvested savings(%)

Result

Tax savings this year

$1,170

Extra growth from reinvesting the savings

$2,058

Loss used to offset gains

$3,000

Loss used to offset ordinary income (max $3,000)

$3,000

Loss carried forward to future years

$2,000

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How to use this

1Enter realized capital loss ($).
2Enter capital gains elsewhere this year ($).
3Enter rate on those gains (short or long-term) (%).
4Enter marginal ordinary income rate (%).
5Enter years you'll keep the tax savings invested.
6Enter expected return on reinvested savings (%).
7Read your tax savings this year on the right — it updates as you type.
8Hit Share to keep the scenario or send it to someone.

About this calculator

Tax-loss harvesting means selling an investment at a loss, immediately using that loss to offset capital gains elsewhere in your portfolio (and up to $3,000 of ordinary income per year if losses exceed gains), then reinvesting in a similar but not 'substantially identical' security to stay invested. This calculator estimates the current-year tax savings from a harvested loss, factoring in the annual $3,000 ordinary-income offset limit and loss carryforward, and separately estimates the deferred tax cost from the lower cost basis you'll carry into the replacement security (since harvesting doesn't erase gains, it defers them). The real benefit isn't the loss itself, it's the tax-rate arbitrage: you get to deduct against your current short-term or ordinary rate now and only pay tax later at (often lower) long-term rates when you eventually sell for good, plus you got to keep the tax savings invested and compounding in the meantime.

FormulaThis-year savings = min(loss, gains-offset needed) × gain rate + min(remaining loss, $3,000) × ordinary rate. Carryforward = loss − amount used this year. Deferred cost = future gain on lower basis × future rate, discounted by years of extra compounding on the tax savings reinvested.

Worked example

Using the values the calculator loads with:

Inputs

Realized capital loss: 8000 $
Capital gains elsewhere this year: 3000 $
Rate on those gains (short or long-term): 15 %
Marginal ordinary income rate: 24 %
Years you'll keep the tax savings invested: 15
Expected return on reinvested savings: 7 %

Results

Tax savings this year: $1,170
Extra growth from reinvesting the savings: $2,058
Loss used to offset gains: $3,000
Loss used to offset ordinary income (max $3,000): $3,000
Loss carried forward to future years: $2,000

What each field means

Inputs

Realized capital loss ($): The realized capital loss used in the calculation, measured in $. Starts at 8000 $ so you have a working example on load.
Capital gains elsewhere this year ($): The capital gains elsewhere this year used in the calculation, measured in $. Starts at 3000 $ so you have a working example on load.
Rate on those gains (short or long-term) (%): The rate on those gains (short or long-term) used in the calculation, measured in %. Starts at 15 % so you have a working example on load. Accepted range: 0–40 %.
Marginal ordinary income rate (%): The marginal ordinary income rate used in the calculation, measured in %. Starts at 24 % so you have a working example on load. Accepted range: 0–50 %.
Years you'll keep the tax savings invested: The years you'll keep the tax savings invested used in the calculation. Starts at 15 so you have a working example on load. Accepted range: 0–40.
Expected return on reinvested savings (%): The expected return on reinvested savings used in the calculation, measured in %. Starts at 7 % so you have a working example on load. Accepted range: 0–15 %.

Results

Tax savings this year: Returned as a money amount in US dollars and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Extra growth from reinvesting the savings: Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Loss used to offset gains: Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Loss used to offset ordinary income (max $3,000): Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
Loss carried forward to future years: Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.

FAQ

What's the wash sale rule I need to avoid?

You can't buy the same or a 'substantially identical' security within 30 days before or after the sale that generated the loss, or the loss is disallowed for tax purposes and added to the basis of the replacement shares instead. Swap into a similar-but-different fund, like moving from one S&P 500 index fund to a total-market fund, to stay invested without triggering a wash sale.

Is tax-loss harvesting free money?

No — it's a deferral, not a permanent tax reduction, because the replacement security carries a lower cost basis, so you'll owe more tax when you eventually sell it (unless you die holding it and heirs get a stepped-up basis, or you donate it). The value comes from the time value of money on the tax savings and the chance to use today's rate against a possibly lower rate later.

Can I harvest losses inside a 401(k) or IRA?

No. Losses inside tax-advantaged accounts have no tax consequence and can't be harvested. This strategy only applies to taxable brokerage accounts.

What if I don't have any capital gains to offset?

You can still deduct up to $3,000 of net capital losses against ordinary income each year, and anything beyond that carries forward indefinitely to future tax years until fully used.

Accuracy and limitations

Results are estimates before tax, fees, and inflation unless an input explicitly covers them.
Rates are treated as fixed for the whole period — variable-rate products will drift from this projection.
This is educational maths, not financial advice. Check anything contractual with the lender or your accountant.

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Cite this calculator

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APA

RevenueLab. (2026). Tax-Loss Harvesting Benefit Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/tax-loss-harvesting-benefit

HTML

<p>Source: <a href="https://www.revenuelab.fyi/toolbox/tax-loss-harvesting-benefit" target="_blank" rel="noopener">Tax-Loss Harvesting Benefit Calculator — RevenueLab</a> (2026).</p>

Markdown

Source: [Tax-Loss Harvesting Benefit Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/tax-loss-harvesting-benefit) (2026).