I'm thinking to take a ride with grab/uber tomorrow. I want to know is the fare stated during booking is final?  I know that uber, if the destination taking longer time to arrive they will have surcharge(for example traffic jam).

But i heard got cases which they incur  sudden surcharge,  like if there are less driver available (even when rider  already on a ride with them and  on their  way to destination ) and the final fare will differ from the one stated in the booking.

Can frequent rider shed a light on this? Need input on both grab and uber. Thanks in advance.