The miners' fee on the Blockchain.

These are fees paid to miners to include a cryptocurrency transaction within a block.
These commissions, also called fees, depend solely on the network that manages the chosen cryptocurrency. Bitnovo neither intervenes nor benefits from this value.

The commission/fee is variable, it is NOT a percentage and does NOT depend on the amount that is sent.
It works as an auction and the price is related to the bytes transmitted, so when there is more traffic on the network is when the commission costs rise the most.

From pages like these you will be able to check, in real time, the commissions of the transactions:

BTC: https://estimatefee.com
BTC: https://btc.network/estimate
BTC: https://bitcoiner.live
ETH: https://ethgasstation.info
ETH: https://etherscan.io/gastracker

Various: http://cryptofees.net

It is a good choice to activate, whenever you can, the RBF option (Replace by fee) that way, if you need to, you can change the mining fee and thus speed up the acceptance of the transaction.

Special care should be taken when choosing a low priority because, although this will result in a low commission, it can delay the delivery for a long time.