Keeping crypto records.

Crypto transactions are final and often spread across multiple platforms, wallets and networks. Without your own records, it becomes nearly impossible after a few years to reconstruct when you bought, sold, swapped or received tokens as a reward. That is not only inconvenient when filing a return, but can also become a problem if the tax authority or another regulator asks for supporting evidence.

A second reason to start early is that platforms disappear, restructure or change their export formats. Anyone waiting until the end of the year, or until filing time, risks finding that historical data is no longer fully available.

For every transaction, it is worth recording at minimum the date, the type of transaction (purchase, sale, swap, receipt as a reward, transfer between your own wallets), the number of tokens, the euro value at that moment, and the platform or wallet involved. When swapping between two cryptocurrencies, it is particularly important to note the value on both sides of the transaction, since a swap is treated as a separately valued event under many tax systems.

Transfers between your own wallets are not purchases or sales and in principle do not change your total holdings, but it is still worth recording them. This avoids accidentally double-counting the same tokens or mistaking an internal transfer for a transaction with a third party.

Most regulated platforms offer an export function for transaction history, usually as a CSV file. These exports vary considerably in quality: some platforms provide a clear overview with the euro value per transaction, while others give only the token amount and a timestamp without a converted value.

For on-chain activity, such as interaction with DeFi protocols or NFT marketplaces, a blockchain explorer is often needed to retrieve the full transaction history of a wallet address. Some specialised tools can link wallet addresses directly and automatically import transactions, significantly reducing manual work.

Cost basis is the euro value you paid for a given amount of crypto, including any transaction fees. This value is the reference point for determining profit or loss on a later sale, and is also relevant when valuing assets on a reference date if the tokens are still held.

When the same token has been bought repeatedly at different times and different prices, the question arises which cost basis applies on a partial sale. Common methods include 'first in, first out' (the oldest purchase is considered sold first) and an average cost basis across all purchases. Which method applies depends on the rules of the relevant country; this is one area where specialist advice can be worthwhile.

Specialised software exists that consolidates transactions from multiple exchanges and wallets, calculates cost basis using different methods, and generates an overview aligned with common tax filing formats. Such tools can save considerable time, especially for anyone active on multiple platforms or regularly using staking, lending or DeFi.

Regardless of which tool you use, it remains sensible to export data periodically, for example monthly or quarterly, and store it outside the platform itself. This builds your own archive that does not depend on the continuity of a single provider.

It regularly happens that someone realises years later that early transactions were not properly recorded, for example on a platform that no longer exists. In that case, it is often still possible to retrieve transactions on a wallet address via blockchain explorers, though the direct link to the euro value at the time of transaction may be missing.

Historical price data for well-known cryptocurrencies is generally available through market data providers, so a value on a specific date can still be reconstructed. This takes more effort than if records had been kept properly from the start, which is precisely the reason not to delay.