Crypto arbitration: taxation in Spain

Crypto arbitrage consists of exploiting price differences of the same asset on different exchanges simultaneously. It's theoretically low risk: you buy where it's cheapest and sell where it's most expensive, capturing the difference. But fiscally, each operation is a taxable event.

Types of crypto arbitrage

1. Exchange Arbitrage (CEX-CEX):

• Bitcoin is trading at €30,000 on Kraken and €30,050 on Coinbase.
• You buy on Kraken, sell on Coinbase instantly.
• Earning: €50 per BTC (less commissions).

2. DEX-CEX Arbitrage:

• ETH is €2,000 on Uniswap and €2,020 on Binance.
• You buy on Uniswap (including gas) and sell on Binance.

3. Triangular:

• BTC/ETH → ETH/BNB → BNB/BTC → if the sequence closes with a profit.

4. Cross-chain:

• Same asset, different chains. Requires bridges.

Each operation is a tax event

Arbitrage generates dozens, hundreds or thousands of trades per day. Every purchase and sale is a tax event. If you use automated bots, you can have millions of events in a year.

The administrative burden is astronomical if you don't have the right tools.

Economic activity or capital gains?

If the arbitration is:

• Sporadic and unstructured: Capital gains, basis of savings.
• Regular, organized, with bots: Economic activity, general basis, personal income tax scale up to 47%.

The line is interpretive, but if you have bots running 24/7, capital dedicated exclusively to this and you see income as a regular main/complementary source, it is most likely economic activity.

The commission trap

Arbitrage seems profitable but commissions can eliminate margin:

• Trading commissions (0.1% each side → 0.2% per operation).
• Gas (Ethereum): may be more than the arbitrage margin.
• Order book spread.
• Slippage running.

Fiscally: Commissions are deductible from the result. A transaction with a net loss (due to commissions) generates a tax loss.

Pegged stablecoin arbitrage

Some stablecoins temporarily “unstick.” For example, USDC at €0.985 on an exchange.

• USDC purchases at €0.985.
• You sell USDC at €1 when the parity recovers.
• Profit: €0.015 per USDC → 1.5%.

This is perfectly valid fiscally. The gain is a capital gain based on savings.

Arbitration risks and their fiscal impact

Execution risk: The price changes while you execute → the trade may close with a loss.
Liquidity risk: You cannot close the other leg of the operation → you lose.
Counterparty Risk: Exchange goes down or has problems.

Losses are deductible, just as gains are taxable.

Arbitration bots: who is the taxpayer?

If you use an automated bot (Hummingbot, running on your server):

• You are the passive subject. The bot is just a tool.
• The bot's profits/losses are yours.
• If the bot operates through a company → the company pays taxes (IS).

If you use a third-party bot ("copy trading" or bot platform):

• It's still your profit/loss.
• But the one on the platform can retain or not.

How to manage the registration of thousands of operations

For high frequency arbitration, it is essential:

1. Export all exchange trades (CSV).
2. Use specific software: Koinly, Blockpit, CryptoTax (multi-exchange support).
3. Verify that the software calculates FIFO correctly between exchanges.
4. Consider hiring a tax advisor specialized in high frequency trading.

Updated: April 2026 | Fiscal year: 2025