Tax Loss Harvesting Calculator

Tax loss harvesting is an investment strategy that involves selling a security that has declined in value below its purchase price (cost basis) to realize a capital loss. That realized loss can then be used to offset capital gains you have already recognized elsewhere in your portfolio — reducing the taxable gain dollar for dollar. Any loss that exceeds your capital gains can further reduce ordinary income by up to $3,000 per year, and leftover losses carry forward indefinitely into future tax years.

The strategy does not eliminate taxes permanently; it defers them. When you sell at a loss and later repurchase a similar (but not identical) security, your new cost basis is lower than your original one. A future gain on that new position will eventually be taxed — but you have enjoyed the time-value benefit of keeping those dollars invested in the interim. In a long portfolio lifetime, systematic harvesting can meaningfully improve after-tax compound returns.

Tax loss harvesting applies to unrealized losses — positions currently worth less than what you paid for them. The loss only becomes "harvestable" when you sell. The IRS requires that you actually complete the sale before December 31 of the tax year in which you want to claim the deduction.

The wash sale rule is the key constraint: if you sell a security at a loss and buy the same or a "substantially identical" security within 30 days before or after the sale, the IRS disallows the loss. The 61-day window (30 days before + sale day + 30 days after) prevents investors from maintaining continuous market exposure while claiming the tax benefit on paper. To harvest a loss validly, either wait 31 days to repurchase, or immediately buy a similar-but-not-identical replacement (e.g., switch from one S&P 500 ETF to a different one tracking the same index).

This tax loss harvesting calculator models the exact IRS mechanics: offsetting capital gains first, then offsetting up to $3,000 of ordinary income, and calculating any carryforward — giving you a clear dollar figure for your potential tax savings this year.

This calculator uses the same step-by-step logic the IRS prescribes for applying capital losses on Schedule D. Enter your investment's current market value and original cost basis to determine the harvestable loss. Then provide your tax situation — other capital gains, federal tax bracket, state rate, and holding period — and the calculator applies the loss in the correct order.

Step 1 — Compute the loss: The harvestable loss equals cost basis minus current market value. If the result is zero or negative, your position has a gain, and there is nothing to harvest.

Step 2 — Offset capital gains: The loss first cancels out any existing capital gains (up to the full loss amount). The tax saved equals the offset amount multiplied by the combined capital gains rate (federal + state). For long-term positions held more than one year, the calculator uses the most common 15% federal long-term rate. For short-term positions held one year or less, it applies your federal ordinary income bracket.

Step 3 — Offset ordinary income: If any loss remains after the capital gains offset, up to $3,000 can reduce ordinary income. Tax saved here equals that offset multiplied by the combined ordinary income rate (federal bracket + state rate).

Step 4 — Carryforward: Any remaining loss beyond the $3,000 ordinary income cap carries forward to future tax years with no expiration. The calculator estimates future value by applying your current combined capital gains rate to the carryforward amount.

Effective loss reduction expresses total immediate tax savings as a percentage of the original unrealized loss, showing how much of your paper loss is "recovered" through the tax system this year.

The federal tax rate on a capital loss offset depends heavily on whether the position was held for more than one year (long-term) or one year or less (short-term). This distinction changes the dollar value of the same loss by a wide margin.

Long-term capital losses first offset long-term capital gains, which are taxed at preferential rates of 0%, 15%, or 20% depending on your income. This calculator uses 15% as the most common long-term rate. If you have no long-term gains, long-term losses can then offset short-term gains (taxed at ordinary rates), but the calculator simplifies to the single combined capital gains rate you specify.

Short-term capital losses offset short-term capital gains first, and those gains are taxed at ordinary income rates — identical to your wage and salary bracket. For a taxpayer in the 32% federal bracket with 8% state tax, a short-term loss is worth 40 cents per dollar of offset versus 23 cents for the same loss on a long-term position. This means harvesting a short-term loss is generally more valuable per dollar of loss.

From a strategy perspective, it is often wise to let winners run long-term while harvesting short-term losers early. The combination maximizes after-tax return: losses are eliminated at high ordinary rates, gains are eventually realized at low long-term rates.

The IRS netting rules on Schedule D require you to net all short-term gains and losses together, and all long-term gains and losses together, before any cross-netting. This calculator provides a simplified model that applies a single capital gains rate to the gains offset, which is accurate for the most common scenario where the loss and gains are the same holding period class.

When your harvested loss exceeds both your capital gains and the $3,000 ordinary income cap in a single year, the unused portion does not disappear — it carries forward indefinitely under IRC Section 1212. There is no time limit, no expiration, and the carryforward retains its original character (long-term or short-term).

In practice, a large unrealized loss — say $20,000 on a concentrated stock position — could generate meaningful tax savings across several future years. The year of harvest, you might save $1,800 from a $5,000 gains offset (at 36% combined rate) plus $1,080 from the $3,000 ordinary income deduction. The remaining $12,000 carryforward is available in Year 2 and beyond, where it will offset future gains or income using that year's tax rates.

This calculator estimates the potential future tax savings from the carryforward by multiplying the carried amount by your current combined capital gains rate. This is an approximation — your actual rate in future years may differ — but it gives you a reasonable lower-bound sense of the long-term value sitting in unused losses.

For investors who realize gains regularly (e.g., rebalancing, selling appreciated real estate, exercising stock options), a large carryforward is extremely valuable. It can shield substantial future income from tax at zero cost, since the loss was already "paid for" by the investment decline. Tracking your carryforward on Form 8949 and Schedule D each year ensures you never leave this deduction unused.

Estate planning note: capital loss carryforwards do NOT transfer to heirs. If you hold a carryforward at death, it dies with you (or stays with a surviving spouse in a joint return scenario). This adds urgency to using carryforwards while alive and in a high tax bracket.

The wash sale rule (IRC Section 1091) is the single most important compliance requirement in tax loss harvesting. If you sell a security at a loss and acquire the same or a "substantially identical" security within 30 days before or after the sale, the IRS disallows the loss. The disallowed loss is not permanently lost — it is added to the cost basis of the replacement security — but you forfeit the current-year timing benefit.

"Substantially identical" is broadly interpreted but not infinitely broad. Individual stocks in the same industry are generally not substantially identical. However, two ETFs tracking the exact same index (e.g., two different S&P 500 index funds from different issuers) may be considered substantially identical by the IRS, though there is no definitive ruling on ETF pairs. The safest approach is to replace with a fund tracking a different but correlated index — for example, swapping a Russell 1000 ETF for an S&P 500 ETF or a total market ETF.

Common tax loss harvesting strategies:

• Fund-pair harvesting: Maintain two lists of similar ETFs. When one falls, sell it and buy the counterpart. After 31 days, optionally swap back.
• Year-end harvesting sweep: Review the portfolio in November/December for any positions with unrealized losses exceeding transaction costs. This aligns with the December 31 deadline for current-year deductions.
• Continuous (automated) harvesting: Robo-advisors monitor portfolios daily and harvest whenever a position falls a threshold amount (e.g., 2%). This captures volatility-driven losses that might reverse before year-end.
• Specific lot identification: When you own multiple lots of the same security at different prices, you can choose to sell the highest-cost lots first (highest-cost, first-out / HIFO) to maximize the loss or minimize the gain on any given sale.

Transaction costs matter. For small losses (under $500), brokerage commissions, bid-ask spreads, and the inconvenience of tracking wash-sale windows may exceed the tax benefit. This calculator's "Small loss — Consider transaction costs" assessment flags positions where the math may not justify the effort.

Tax loss harvesting is not universally beneficial. Several situations argue against harvesting even when an unrealized loss exists:

Low tax bracket now, high bracket later: If you expect to be in a higher tax bracket in retirement or in coming years, deferring the loss (letting the position recover) means a future gain is taxed at a lower rate. Harvesting now at a 12% bracket to save $240 on a $2,000 loss, only to face a future gain taxed at 24%, may net negative after the embedded gain in the replacement position is realized.

Transaction costs and complexity: In taxable accounts with small balances, the administrative burden of tracking wash-sale windows, adjusted cost bases, and carryforward schedules may not be worth the tax savings. Automated platforms handle this seamlessly; manual investors should weigh the time cost.

State tax differences: Some states (e.g., California) do not conform to the federal $3,000 ordinary income deduction cap, or have different carryforward rules. Always verify your state's treatment separately.

AMT (Alternative Minimum Tax): Under the AMT, capital losses may be treated differently. Investors subject to AMT should consult a tax advisor before aggressive harvesting.

Retirement accounts: Tax loss harvesting only applies to taxable brokerage accounts. Losses inside an IRA, 401(k), or other tax-advantaged account have no tax impact and cannot be harvested.

This calculator is for educational estimation only. The actual tax impact depends on your full tax picture, lot-level holding periods, state-specific rules, AMT exposure, and other factors. Consult a qualified tax professional before executing a harvesting strategy.