Call forwarding is a two-step process.
First, an incoming call will be received on your CallHippo number therefore incoming calling charges for this call would be charged.
Click on this link to see incoming call charges:- https://callhippo.com/global-number-charges/
Then that call will be forwarded from your CallHippo number to the number you forward the call to and therefore outgoing calling charges for this transfer of calls will be charged.
Click on this link to see outgoing call charges:- https://callhippo.com/outbound-calling-charges/