If the cost-basis of your disposal is $0 then you can refer to these articles instead:
Gains are too high
Missing purchase history (missing costs)
It's common that a cost-basis might seem wrong even if it actually isn't.
Scenario: You deposited 1 BTC worth 1000 USD into a wallet and withdrew it later but the cost-basis on the withdrawal transaction doesn't match the cost of the 1 BTC (1000 USD).
This is because Koinly is using a universal pool that consists of all your BTC to determine the cost. If you want to separate the cost-basis in each of your wallets you can enable "Wallet-based cost tracking" on the Settings page.
Refer to the article on cost-tracking method for more info.
Pro tip: You can look at the Cost Analysis for any disposal to see how the cost-basis has been calculated. You can find the Cost Analysis by clicking on the transaction (only available for paid users)
Other common reasons why a cost-basis might be different from the expected cost-basis:
Bed and Breakfasting rule (UK only)
Superficial loss rule (Canada only)
The 4 week rule (Ireland only)
FIFO (First In, First Out):
Looking at the example above, it is pretty clear that the user lost $100 but he still has a lot of gains (?)
This is because of the FIFO cost-basis method that is being used to calculate the cost-basis. The user has some other ETH tokens in his account and those tokens are older than this recently purchased ETH. The FIFO method will always choose your oldest assets first when deciding which of your tokens to use for the cost-basis. In the example above, the user had another ETH token that was purchased earlier for $1908. After these trades, the user will have 1 ETH remaining in his account and the cost-basis for that 1 ETH would be $3000.
ACB (Average Cost Basis / Adjusted Cost Base)
If using ACB, the example shown above would be very similar. The main difference is that the cost of the 2 ETH would be averaged so that the cost-basis of the sale would be $2454 and the gains would therefore be lower. The cost-basis of the remaining 1 ETH would also be $2454!