How to predict race time during activity?

Hello everyone

I'm getting stucked to find a way to show in a data field the race time of a running activity. I will try to explain myself better. In a run activity I can choose a workout, and Fenix knows total distance I've to do. So I hope, using average pace, Fenix can show me total expected time at the end of the workout.

For example if I load a marathon workout in which total distance i s 42.195 meters, when I'm running  at 4:40/km of average pace, I would like to see 3:17:00 as total time of the workout. If the average pace change, the global time changes too.

It's about two days I'm trying to find this information, but it seems to be not possibile. Does Anyone knows how to find this information?

Many thanks to anyone who answers.

Roberto