Cost basis is what an asset cost you: the purchase price plus any commission or other costs of buying it. When you sell CryptocurrencyCryptocurrencyA digital currency secured by cryptography and recorded on a shared ledger, with no bank or government issuing or controlling it., your capital gainCapital gainsThe profit from selling an asset for more than it cost you; for individuals in Iceland, gains on crypto are taxed as capital income. is the difference between the sale price and the cost basis. So the cost basis decides how much of the sale price counts as profit. The Icelandic term is stofnverð.
How is the cost basis of crypto worked out?
Skatturinn, the Icelandic tax authority, describes these rules among others:
- Crypto you bought. The cost basis is the purchase price plus handling costs or commission.
- Buying in batches. If you have bought the same crypto several times at different prices and sell part of it, the cost basis is the average purchase price.
- Swaps. If you swap one crypto for another, the market value in krónur at that moment applies. That amount is both the sale price of what you give up and the cost basis of what you receive.
- Mining. The cost basis of crypto from MiningMiningThe process in which computers compete to solve a puzzle so they can add the next block to the blockchain and earn new bitcoin and fees. is its value when it was mined. If it was never declared as income, the cost basis is ISK 0.
A simple example
These figures are made up and only show the method. You buy some crypto and pay ISK 200,000 including commission. Later you buy the same amount of the same crypto and pay ISK 300,000. Your total cost basis is then ISK 500,000.
If you sell half, its cost basis is the average purchase price, ISK 250,000. The half you keep has the same cost basis, ISK 250,000.
What to keep in mind
A cost basis is like a receipt: without it, you don't know what you paid. So keep a record of the date, amount, price in krónur and commission for every trade. The average purchase price is based on every purchase of the same crypto, possibly many years back. You show the calculation on an attachment to your tax returnTax returnThe yearly report to Skatturinn on last year's income and your assets and debts at year end. Crypto must be declared, even if you sold nothing..
These are the general rules as Skatturinn describes them (in Icelandic). Talk to your accountant or Skatturinn about your own situation.
Everything in Myntkaup Learn is written and regularly reviewed by the Myntkaup editorial team. It is for education and is not investment advice. Editorial policy. Updated 18 October 2026.