How to Calculate Crypto Loss Harvesting Before Year End

What Loss Harvesting Actually Does to Your Tax Bill

Crypto loss harvesting is a mechanical process. You sell a depreciated asset before December 31, realize the loss on paper, and use that loss to offset capital gains elsewhere in your portfolio.

The IRS taxes short-term crypto gains (held under 12 months) at ordinary income rates. Those rates reach 37% at the top bracket. Long-term gains top out at 20%, plus the 3.8% Net Investment Income Tax for high earners. A single harvesting decision on a $40,000 unrealized loss can translate into $14,800 in tax savings for a 37% bracket filer.

That number is not hypothetical. It is the math. The question is whether you run it before December 31 or miss the window entirely.

The Core Formula

Loss harvesting math starts with three inputs.

Realized gain = Sale price minus cost basis

Net capital position = Sum of all realized gains minus sum of all realized losses

Tax owed = Net capital position multiplied by your applicable rate

If your net capital position is positive, harvesting additional losses reduces it. If it is already zero or negative, further harvesting has diminishing value beyond the $3,000 annual deduction against ordinary income.

Every decision branches from those three calculations.

Step 1: Establish Your Cost Basis Before You Sell Anything

This is where most investors make the mistake that triggers audits.

Cost basis for crypto is the original purchase price plus any fees paid at acquisition. If you bought 2 ETH at $1,800 each and paid a $12 network fee, your total cost basis is $3,612, not $3,600.

When you hold multiple lots of the same token purchased at different prices, the IRS allows three accounting methods:

• FIFO (First In, First Out): Oldest lots sell first. Produces the largest gains in a rising market.
• LIFO (Last In, First Out): Newest lots sell first. Rarely optimal.
• Specific Identification: You designate exactly which lot you sell. This gives the most control and, in most cases, produces the best tax outcome.

Specific identification requires contemporaneous records. You must document the lot, the acquisition date, the acquisition price, and the sale before or at the time of the transaction. If your exchange does not support lot-level records, maintain a spreadsheet and download transaction CSVs before year end.

Why Accounting Method Changes the Outcome Dramatically

Assume you hold 5 BTC purchased across three lots:

• Lot A: 2 BTC purchased at $58,000 each. Total basis: $116,000.
• Lot B: 2 BTC purchased at $38,000 each. Total basis: $76,000.
• Lot C: 1 BTC purchased at $22,000. Total basis: $22,000.

Current market price: $42,000 per BTC.

You sell 2 BTC.

Under FIFO, you sell Lot A. Proceeds: $84,000. Basis: $116,000. Loss: $32,000.

Under specific identification selecting Lot C and one BTC from Lot B, you sell 1 BTC at $22,000 basis and 1 BTC at $38,000 basis. Proceeds: $84,000. Basis: $60,000. Gain: $24,000.

Same sale. Same market price. A $56,000 swing in taxable outcome depending on which lot you designate. FIFO produces the larger loss here. But if your goal is to offset $24,000 in gains elsewhere, FIFO over-harvests. That excess loss carries forward, which is not inherently bad, but it means you sold assets you could have held.

The correct approach is to calculate your target loss first, then select the lot that delivers exactly that amount.

Step 2: Calculate Your Net Capital Gain Position

Before you harvest, you need a current-year profit and loss statement across every taxable account.

Pull every realized transaction from January 1 through today. Include:

• Crypto sales and swaps
• Stock sales
• Real estate capital gains distributions from funds
• Any other Schedule D items

Separate short-term and long-term columns. They offset within their own category first, then cross-offset if one column produces a net loss.

Example: You have $18,000 in short-term gains from crypto trades executed in March. You have $6,000 in long-term gains from an ETF sale. Your combined net gain is $24,000.

To eliminate the tax on that $24,000, you need $24,000 in net capital losses before December 31.

If you hold unrealized crypto losses of $31,000 across several positions, you do not need to sell all of them. Sell enough to generate $24,000 in recognized losses. The remaining $7,000 in unrealized losses stays in your portfolio, uncrystallized, available for a future year.

Step 3: Work a Full Harvesting Scenario

Here is a complete worked example with real numbers.

Portfolio snapshot, mid-December:

• Ethereum position: Purchased 3 ETH at $3,200 each. Current price: $2,100. Unrealized loss: $3,300. Holding period: 8 months (short-term).
• Solana position: Purchased 120 SOL at $175 each. Current price: $88. Unrealized loss: $10,440. Holding period: 14 months (long-term).
• Polygon position: Purchased 8,000 MATIC at $0.90 each. Current price: $0.52. Unrealized loss: $3,040. Holding period: 5 months (short-term).

Realized gain position so far this year:

• Short-term gains: $9,800
• Long-term gains: $7,200

Target losses needed:

• Short-term losses needed: $9,800 (to zero out short-term gains)
• Long-term losses needed: $7,200 (to zero out long-term gains)

Harvesting plan:

Sell the Ethereum position. Realizes $3,300 in short-term loss. Sell the Polygon position. Realizes $3,040 in short-term loss. Combined short-term losses: $6,340. Still $3,460 short of zeroing short-term gains.

Sell 39.77 SOL (at current price of $88). Proceeds: $3,499.76. Basis: 39.77 SOL times $175 equals $6,959.75. Loss: $3,459.99. This is a long-term loss applied to offset the remaining short-term gain deficiency. Per IRS netting rules, excess long-term losses offset short-term gains after short-term losses are exhausted.

Net short-term gain after harvesting: approximately $0. Long-term gains remaining: $7,200. Partially offset by the remaining Solana position's long-term losses. You still hold 80.23 SOL, with a remaining unrealized long-term loss of $6,980.01. Sell 79.77 SOL (loss: $6,980) to eliminate the long-term gain position entirely.

Tax savings at a 32% short-term rate and 15% long-term rate:

• Short-term tax eliminated: $9,800 multiplied by 0.32 equals $3,136.
• Long-term tax eliminated: $7,200 multiplied by 0.15 equals $1,080.
• Total tax saved: $4,216.

And because the wash-sale rule currently does not apply to crypto, you can repurchase ETH, SOL, and MATIC immediately after selling. You maintain your market exposure. You pocket $4,216 in tax savings.

The Wash-Sale Rule: What Changes in 2026 and Beyond

Congress has proposed applying wash-sale rules to digital assets in multiple budget bills. None have passed as of this writing. But the risk is real.

If wash-sale treatment becomes law, the 30-day repurchase window would nullify the loss. A same-day repurchase strategy that works in 2025 could produce zero tax benefit in a future year.

Monitor legislative updates through November. If wash-sale rules pass mid-year, adjust your harvesting strategy to respect the 30-day window.

What to Do With Losses That Exceed Your Gains

The IRS allows a maximum $3,000 deduction of net capital losses against ordinary income per year. Losses beyond that carry forward indefinitely.

If your harvested losses total $19,000 and your gains total $12,000, your net loss is $7,000. You deduct $3,000 against ordinary income this year. The remaining $4,000 carries to 2027, where it offsets future gains at full value.

Loss carryforwards are assets. Track them in your tax records each year. A $4,000 carryforward in the 37% bracket is worth $1,480 in future tax savings.

Run the Numbers Before You Execute

The single most costly mistake is selling first and calculating second. Sell decisions cannot be undone inside the same tax year once the transaction settles.

Build your full-year gain and loss picture first. Identify the exact loss amount you need. Select the specific lots that deliver that amount using specific identification. Then execute.

The CalcMoney Income Tax Calculator lets you model this scenario before you place a single trade. Input your current income, your realized gains, and your planned harvesting amount. The calculator shows your marginal rate, your estimated tax owed, and the after-harvesting savings in real dollars.

Run your scenario now, while positions are still open and the year-end window remains.

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