When a transaction is broadcasted to the network, it has to wait to be included in a block by the miners. Once a transaction has been included in a mined block, the transaction has received one confirmation. With each subsequent block, the number of confirmations increases for the transaction.

To avoid the risks of double spending, funds aren’t credited until a certain number of confirmations have taken place (as listed below).The more confirmations received, the more permanent and irreversible the transaction is.

Each block is found at a different rate depending on the blockchain.

For example, on the Bitcoin blockchain, a block is mined on average every 10 minutes, and Kraken only credits Bitcoin deposits to a client’s account after four confirmations, which takes approximately 40 minutes. 

However, sometimes it can take Bitcoin miners 30 or even 60 minutes to mine a single block (one confirmation). This is outside of Kraken's control.

Each cryptocurrency has a different minimum amount needed to deposit at Kraken.