Cryptocurrency transactions: why October is the time to review their tax implications

How are cryptocurrency transactions taxed?

The sale of cryptocurrencies in exchange for euros or another legal tender may result in a capital gain or loss for personal income tax purposes. Generally speaking, the gain or loss is determined by the difference between the sale price and the purchase price, taking into account any expenses directly related to the transaction and incurred by the taxpayer.

This rule does not apply solely when crypto-assets are converted into euros. The exchange of one cryptocurrency for another also constitutes a transaction capable of generating a capital gain or loss, even if the funds have not passed through a bank account.

Therefore, to determine the tax result for the financial year, it is not sufficient simply to review the withdrawals made during the year. It is necessary to reconstruct the sales and exchanges, identify the assets transferred and calculate the result corresponding to each transaction.

When homogeneous cryptocurrencies acquired at different times are partially transferred, the Tax Authority considers the units acquired earlier to have been sold first, even when the transactions have been carried out via different exchange platforms.

What to review between October and December

The review of the final quarter must be based on a comprehensive overview of the activity carried out during 2026. Among other aspects, it is advisable to analyse:

Transactions carried out during the financial year

The first step is to compile a list of sales, swaps and other tax-relevant transactions carried out during the year.

The information must cover all platforms, wallets and accounts used. Limiting the analysis to a single platform may provide an incomplete picture, particularly where transfers have been made between different providers or assets have been acquired at different times.

Accumulated gains and losses

Each sale or swap transaction may yield a different result. It is therefore necessary to calculate gains and losses individually and subsequently determine the cumulative balance for the financial year.

This review enables you to ascertain, before the end of December, whether the transactions carried out during the year have resulted in a positive or negative net position and what impact this may have on your income tax liability.

Unrealised losses from previous financial years

It is also necessary to check whether there are any capital losses from previous years that remain to be offset.

Personal income tax regulations allow negative balances from capital gains and losses to be offset against gains in the following four years. These offsets must be made up to the maximum amount permitted in each financial year and cannot be carried forward to subsequent years once this period has elapsed.

Reviewing the year in which the losses arose helps to identify whether any of them are about to become ineligible for set-off.

Available documentation

Tax analysis depends largely on the quality and traceability of the information. It is advisable to keep records of transactions, transfers between wallets, proof of purchase and sale, fees and any other documentation that allows the origin and history of the assets to be reconstructed.

Where several platforms have been used or numerous transactions have taken place, organising this information in advance facilitates subsequent calculations and reduces the risk of omissions or inconsistencies.

The importance of acting before 31 December

Decisions taken after the end of the financial year no longer affect the tax liability for 2026. For this reason, the analysis must be carried out well in advance during October, November and December, as these months represent the last opportunity to review the transactions carried out during the financial year. This allows you to assess, with sufficient information, the tax impact these will have on your next income tax return.

It is not a matter of automatically selling assets to generate losses or gains. Any decision must be based on a prior analysis that takes into account the composition of the portfolio, acquisition costs, transactions already carried out, outstanding losses, and the financial and tax consequences of a potential disposal.

An early review enables proper tax planning before the end of the financial year and allows decisions to be made with full knowledge of their financial and tax implications.

Who should review the tax treatment of their cryptocurrencies before the end of the year?

This review may be of interest to taxpayers who:

• Have sold cryptocurrencies during 2026.
• Have exchanged one cryptocurrency for another.
• Trade via several platforms or wallets.
• Have carried out a large number of transactions.
• Have capital losses from previous tax years that remain to be offset.
• Do not have a consolidated calculation of their transactions.
• Need to reconstruct the history and traceability of their assets.

The appropriateness of adopting one measure or another will always depend on the taxpayer’s specific circumstances and the outcome of a comprehensive analysis of their tax position.

E | Advisory, specialist tax advice on crypto-assets

At E Advisory, we analyse the transactions carried out during the financial year, the gains and losses generated, and outstanding balances from previous years.

This work is carried out in coordination with ECIJA Tech’s specialist crypto-asset team, enabling us to combine technological and transactional analysis with the applicable tax treatment.

The aim is to provide the taxpayer with a consolidated overview of their situation before the end of the financial year, to identify any potential issues and to ensure that transactions are declared fully and consistently.

If you have carried out cryptocurrency transactions during 2026 or have losses from previous financial years still to be offset, our team can help you review the information and assess the appropriate actions to take before the end of the year.