For most US retail investors, "tax-loss harvesting" is a phrase associated with stock and ETF portfolios. The mechanic is simple: at the end of the tax year, you sell positions that are below cost, realising the loss, and the loss offsets gains realised elsewhere in the same year (or up to $3,000 of ordinary income, with the rest carried forward, per Publication 550). The constraint is the section 1091 wash-sale rule, which disallows the loss if you buy back substantially identical securities within 30 days.
Crypto is, for now, treated differently. The IRS treats convertible virtual currency as property, not a security, per Notice 2014-21. Section 1091 only applies to securities. The Joint Committee on Taxation has flagged this as a loophole in JCX-2-22, and Congress has tried, in three separate proposals, to extend the wash-sale rule to crypto. None of the proposals have passed as of early 2026, and the loophole is still open for the 2026 tax year.
This article is a checklist for how to use it well in December, where the deadlines are, and the trap to avoid.
The mechanic, plainly
You hold 0.5 BTC at a cost basis of $90,000 per coin. The current spot price is $70,000, so the position is sitting on a $10,000 unrealised loss. You also realised a $12,000 gain earlier in the year by selling some ETH that had appreciated.
If you do nothing, you owe tax on the full $12,000 ETH gain at the applicable capital gains rate.
If, before 31 December, you sell the BTC and immediately re-buy it, you have realised a $10,000 loss that nets against the $12,000 gain. Your taxable gain for the year is now $2,000 instead of $12,000. At a 24% marginal rate the saving is $2,400 of tax. The economic position is unchanged: you still hold 0.5 BTC; the difference is that your cost basis is now $70,000 per coin instead of $90,000.
That last sentence is important. The "saving" is really a deferral, not a permanent escape. If BTC recovers to $100,000 next year and you sell, you will have a $30,000 gain instead of $10,000. The economics work out to a permanent saving only if your future tax rate is lower, or if you eventually die holding the asset and your heirs receive a stepped-up basis under Publication 559. Most of the time it is a deferral that is still worth doing because the deferred tax dollars compound in the market for you instead of in the Treasury.
The December checklist
- Pull a cost-basis report for every wallet you control. Per the per-wallet rule in Revenue Procedure 2024-28, each wallet has its own basis pool. A coin held at one exchange may be in a loss; the same coin at another exchange may not be.
- List every realised gain you already have on the books for the year. Stock gains, ETF gains, crypto gains. Losses can offset gains across asset classes, so the relevant number is the total net gain, not the crypto-only gain.
- Identify lots in a real, materially-meaningful loss. Lots underwater by less than $50 are usually not worth the transaction cost of harvesting once spreads, fees and the price slippage of selling and re-buying are included.
- Decide whether you actually want to keep the position. Tax-loss harvesting is not a reason to sell something you would not otherwise hold. The point is to reset the cost basis on a position you intend to keep.
- Sell the loss-making lot. Use specific identification. Most exchanges let you pick the lot at the time of the sell order; if not, the calculator you use to file should let you map the disposal to a specific acquisition lot.
- Re-buy. Immediately, or wait. See the next section.
- Save the trade confirmations. Both legs. Time-stamped. The IRS will accept screenshots and CSV exports as records, but only if they show the actual trade prices and times.
The "immediately or wait" question
Stock investors who use tax-loss harvesting must wait 31 days before re-buying the same security, or the loss is disallowed. Crypto investors are not currently bound by that rule, so the textbook answer is to re-buy in the same minute, locking in the loss with effectively no market exposure. That is what most automated harvesting tools do.
The risk to be aware of is that this is the most-discussed loophole in retail crypto tax for a reason. The IRS has not extended section 1091 to crypto, but it has signalled in a 2020 GAO report that "economic substance" arguments could in principle be applied to disallow losses on transactions whose only purpose was the tax benefit. To date no high-profile case has tested this in court. A conservative reading of the position is to leave a small, non-zero gap between the sale and the re-buy. Five minutes is not enough; an hour probably is. Different advisers will give different answers and we are not your tax adviser; the legal position as of early 2026 is that there is no statutory minimum gap.
Where harvesting backfires
You harvest into a position you did not really want. Crypto markets are volatile. Selling a loss and re-buying inside the same hour, into a falling price, can give you a worse entry than if you had not touched it. Harvesting is a tax tool, not an alpha tool.
You wash-trade across wallets that the IRS treats as the same taxpayer. Sending a coin from your hot wallet to your cold wallet is not a sale. The IRS does not care which wallet of yours the coin sits in; harvesting requires an actual disposal at market.
You ignore the loss limit on ordinary income. Net capital losses can offset capital gains in full and up to $3,000 of ordinary income per year per Publication 550. Beyond that they carry forward. Realising a $50,000 crypto loss in a year you have no gains to offset is still useful, but the benefit takes years to flow through unless you generate gains to use it against.
Doing the maths in advance
The hardest part of running a December tax-loss harvest is identifying which lots are actually in a loss across multiple exchanges and wallets, and quantifying what each one would save you. That is exactly the calculation the SafeFinance Tax-Loss Harvesting tool exists to do: it takes your raw exchange CSVs, runs the per-wallet FIFO engine, scores every open lot against the current spot price, and produces a sorted list of which positions to sell first to maximise your harvested losses.
The free preview will tell you the headline number - how much you could save - without showing the per-lot detail. Most retail crypto portfolios with even modest activity will surface a number worth at least a few hundred dollars by the time we get to December. For a portfolio actively trading through 2026, the number is often four figures.
Whatever tool you use, the deadline is hard. The IRS counts the trade by the date of execution, not the settlement date. A sale on 31 December at 23:59 UTC counts in the current tax year; the same sale at 00:01 UTC on 1 January does not. Set a calendar reminder for the 28th, not the 31st, so you have a buffer for any platform issues.