You have the choice of 3 dynamic fees (Low / Normal / Priority) that automatically adjust according to the state of the Bitcoin network. When sending, you can also choose the fee option "default", which overrides all that and uses the value from the settings page on Android. iOS users can set the value for the "default" option by selecting .../change fee on the transaction confirmation page.
Bitcoin Fees are set at .0001 BTC per kilobyte by default in Coinomi. Bitcoin transactions are typically around 250 bytes, but this can vary widely. For a typical transaction that is around 250 bytes, the user will pay 0.00002500 BTC (0.0001BTC*0.25).
Default Fee = Transaction Size (in Kilobytes) * .0001 BTC
How is this transaction size calculated?
1. Inputs: For each input address that your transaction sends from, the size will increase by 180 bytes (plus or minus 1). For example, if you have 0.1 BTC on five different addresses, and you want to send all 0.5 BTC in one transaction, then you will be using all five inputs. This will add approximately 900 bytes (180*5) to your transaction size.
2. Outputs: For each output that your transaction sends to, the size will increase by 34 bytes. This will always be 34 bytes in Coinomi as you can only send to one address.
3. Base Size: A base size of 10 bytes is included in every transaction.
Transaction Size (in bytes) = (Inputs x 180) + (Outputs x 34) + 10
Notes: The fees may differ by a few bytes due to the type of input address(es) you use. Bitcoin forks and many similar coins follow this fee structure. Alternatively, Ethereum and other contract-based coins follow another fee structure. You can learn more about Ethereum fees in Coinomi here.
You can also estimate your fees here: