KoinlyticsThis is not tax advice. Tax loss harvesting rules vary by jurisdiction and change often, so check the current year's rules where you file before acting on anything here.
The mechanism
Tax loss harvesting means selling an asset that is worth less than what you paid for it, on purpose, to realize a capital loss you can use against gains. Nothing about the position changes economically until you sell: an unrealized loss sitting in your wallet does nothing for your tax bill. Selling converts it into a realized loss that most jurisdictions let you net against realized gains in the same tax year. For what counts as a disposal and how cost basis is tracked in the first place, see crypto taxes basics; this chapter assumes you already know that ground.
How the offset works
Say you have $10,000 of realized gains this year from trades that went well, and a token position sitting at a $4,000 unrealized loss. Selling that position realizes the $4,000 loss and cuts your taxable gain to $6,000. In the US, capital losses first offset capital gains of the same character, short term against short term and long term against long term, with excess crossing over, and if losses exceed gains, up to $3,000 of the remainder can offset ordinary income each year, with anything left over carried forward indefinitely. Other jurisdictions structure this differently: the UK lets losses offset gains realized in the same tax year and carries forward unused losses, but does not let capital losses offset ordinary income at all. Confirm the offset rules and caps for your own jurisdiction and the current tax year rather than assuming the US structure applies.
Timing: harvesting before the year closes
Because the offset is calculated per tax year, timing matters more as the year end approaches. A loss realized on December 31 counts for that tax year; the same sale on January 2 pushes the benefit a full year out. This is why harvesting activity clusters in the weeks before a tax year closes: holders look at realized gains for the year to date and decide how much unrealized loss to crystallize to bring the net figure down. The trade-off is that selling into a known deadline, in a market where other holders are doing the same thing with the same losing tokens, can depress the price further right when you are trying to exit.
The wash sale question, and why the answer is not fixed
In the US, the wash sale rule under Internal Revenue Code section 1091 disallows a loss deduction if you sell a security at a loss and buy a substantially identical one within 30 days before or after the sale. Section 1091 refers to stocks and securities, and the IRS has classified crypto as property rather than a security since Notice 2014-21. As a result, the wash sale rule has historically not applied to crypto in the US: you can sell a token at a loss and buy it back moments later, keeping your market exposure while still realizing the loss for tax purposes.
This gap has not gone unnoticed. Legislative proposals to extend the wash sale rule to digital assets have been introduced repeatedly, including provisions in the 2021 Build Back Better Act that passed the House but stalled in the Senate, and in successive administration budget proposals since. None had become law as of this writing, but the direction of travel is consistent and the gap could close in any future tax year. Do not treat the absence of a crypto wash sale rule as a permanent feature. Check current law for the specific tax year before repurchasing a harvested position.
The UK contrast: bed and breakfasting and share pooling
The UK never had this gap to begin with, for crypto or shares, and it shows what happens once the loophole is closed. HMRC applies the same matching rules to crypto disposals as it does to shares: a same-day rule, then a 30 day rule. If you sell a token and buy back the same token within 30 days, the disposal is matched against that reacquisition rather than against your original pooled cost basis. If the price has not moved between the sale and the buyback, no loss survives the matching: you have not achieved anything except paying a spread twice. This is the same bed and breakfasting restriction that closed the equivalent trick for UK share portfolios decades ago.
UK crypto holdings also use share pooling: identical tokens you hold are merged into a single section 104 pool with one average cost, rather than tracked as discrete lots the way US cost basis methods allow. That matters for harvesting because you cannot cherry-pick a specific high-cost lot to sell while keeping cheaper ones, the way FIFO or specific-identification lot selection lets a US filer do. A UK sale harvests against the pooled average, full stop.
Cost basis resets: pushing the tax bill forward, not eliminating it
Repurchasing after a harvest resets your cost basis to the repurchase price. If the token later recovers to its original price, the entire recovery becomes a taxable gain, whereas if you had simply held through the dip, that same recovery would have stayed unrealized and untaxed until you eventually sold. Tax loss harvesting is a timing and rate arbitrage, not a way to make a loss disappear: it converts a future, uncertain tax event into cash savings now, and shifts a larger deferred gain onto the position you repurchased. Whether that trade is worth it depends on your marginal rate now versus your expected rate later, and on how much of the eventual gain you plan to realize rather than hold long term.
The risk of harvesting a position you meant to keep
A harvest only preserves your market exposure cleanly where an immediate, penalty-free repurchase is available. Where a wash-sale-style rule applies, like the UK's 30 day rule, you face a choice: wait out the window and take price risk on a name you wanted to hold, or buy a correlated but not identical asset to keep similar exposure, which is a different position with its own risk. If you do plan to rebuild a position after a wait-out period, planning the reentry rather than guessing a single price is worth the extra step; a DCA calculator can model what phasing the buy back in over several dates would have cost against a single lump reentry. Either way, the keep-the-position-just-harvest-the-loss pitch only works cleanly in jurisdictions and tax years where nothing prevents an immediate identical rebuy, and that condition is not guaranteed to persist.
Fees, slippage, and illiquid tokens
A round trip sale and rebuy costs money: exchange spread, DEX slippage, and gas on both legs. On a liquid token like ETH or a major L1 asset this is usually a rounding error. On a thin altcoin, slippage and spread can easily run 1 to 3 percent each way. Work the numbers before harvesting a small position: a $2,000 holding with a $500 unrealized loss, harvested at a 20 percent marginal rate, saves roughly $100 in tax. If the round trip costs 3 percent of position size each way, that is $120 in trading costs alone, before gas. The harvest loses money on paper before it saves a cent in tax. Illiquid positions need a materially larger loss, or a materially cheaper venue, before harvesting clears its own costs.
Practical steps
- Total realized gains for the tax year to date before deciding how much unrealized loss is worth crystallizing.
- Check whether your jurisdiction currently applies any wash-sale-equivalent rule to crypto, and check again each tax year since this is an active area of legislative proposals in the US.
- If your jurisdiction pools cost basis by asset rather than by lot, remember you cannot selectively harvest a single expensive lot.
- Estimate round trip trading costs against the tax saved before harvesting a small or illiquid position.
- Confirm with a local tax specialist before year end filings, since harvesting decisions are hard to unwind after the fact.
- Koinlytics tracks realized and unrealized P&L across wallets and chains, which helps surface which positions carry an unrealized loss worth reviewing, though it does not calculate tax liability or file anything.