🌍 Everywhere · 7 min
The cost basis trap: why missing crypto records can cost you thousands
If you cannot prove what you paid for your crypto, the tax office may treat the entire sale as profit. How it happens and how to avoid it.
Tax is paid on the gain: the selling price minus what the coins cost you. That cost — the cost basis — is something you have to prove. When you cannot, the tax office is free to make its own estimate, and in practice that estimate can be zero.
A simple example
You sell crypto for €20,000 that you originally bought for €15,000. With documented history the taxable gain is €5,000.
Without records, the same sale may be assessed as €20,000 of gain — four times the tax, possibly plus interest and surcharges.
Denmark
Gains are taxed as personal income, which can reach around 52%, while losses only give a deduction of roughly a quarter of their value. SKAT may set the purchase price at zero when it cannot be documented, so every missing record directly raises the bill.
Greece
Gains are taxed at 15%, but money arriving in your bank account from crypto that you cannot explain may be examined as unjustified increase of wealth (πόθεν έσχες) and taxed at much higher income rates.
Where records go missing
Closed or bankrupt exchanges, old wallets, transfers between your own accounts that look like sales, and fees counted twice. Each gap breaks the chain from purchase to sale.
How to protect yourself
Download full exports from every exchange while you still can, keep a list of your wallet addresses and pair transfers between your own accounts. Correcting earlier years on your own initiative is generally treated far more leniently than errors found in an audit.