I have a bitcoin core running on testnet, so for suppose I have a wallet balance of **1BTC** and I have to send it to an address**x**, so how can I know the amount of transaction fee so that I can subtract it from the sending amount.

```
bitcoin-cli sendtoaddress x 1

```

This will return an error stating that 

```
error code: -4
error message:
Error: This transaction requires a transaction fee of at least 0.00000488

```

How can I know it beforehand the fee required for a transaction?