1. The universal pattern (with local exceptions)
Nearly all tax authorities treat crypto as property or an asset, not currency. That means: every disposal - selling for fiat, trading BTC for ETH, spending crypto on goods - is potentially a taxable event where you compute gain/loss = proceeds − cost basis. Some jurisdictions exempt small gains, some have holding-period reductions, a few treat certain transactions differently. The pattern is universal; the parameters are local.
2. What triggers a taxable event
Typically taxable: crypto→fiat, crypto→crypto (yes, even without your currency), crypto→goods/services. Typically not yet taxable: buying crypto (the event is the disposal, not the purchase), transfers between your own wallets (document them anyway - exchanges report gross flows). Moves between exchanges of different types (spot vs. derivatives accounts) can be treated differently - check locally.
3. Cost basis and holding period
Cost basis = what you paid, including fees. When selling part of a position, jurisdictions differ: FIFO is the common default; some allow LIFO or specific identification - and the choice can halve or double the tax. Holding period matters in many countries: Germany's famous 1-year exemption (private sales), US long-term vs. short-term rates, France's flat rate after its holding-period regime. The holding period is the biggest single lever most retail traders never plan for.
Remember: Documentation is the tax strategy. Export trades monthly (CSV), record wallet transfers, keep fee receipts. An unprovable cost basis defaults to zero - meaning you pay tax on the full proceeds.
4. Staking, lending, airdrops: the fringe cases
These vary most between jurisdictions: staking rewards can be income at receipt (with the receipt value as new cost basis) or taxed at disposal; airdrops range from untaxed to income at market value; interest from lending is income nearly everywhere. Derivatives and margin gains often fall under different (sometimes loss-restricted) regimes than spot. These rules are also the ones that change most often - re-verify yearly.
5. The country map (high level, verify locally)
US: property treatment, short/long-term rates, $3,000 annual capital-loss offset. Germany: private-sale regime; 1-year holding = tax-free; staking/lending requires 10-year holding for the exemption. Austria: flat ~27.5% on gains since 2022. Switzerland: private capital gains untaxed (wealth tax applies); staking income taxed. UK: capital gains with annual allowance, crypto-to-crypto taxable. France: flat rate regime with exceptions. Portugal: historically friendly, tightened recently. UAE: no personal capital-gains tax currently. None of these paragraphs is advice - each is a pointer to what to ask a local professional.
Risk: Tax evasion in crypto is not a gray area - exchanges report under DAC8/CRS-style frameworks, and blockchains are permanent records. The realistic cost of "not declaring" is penalties plus interest on top of the tax you owed anyway.