When you are creating and then saving an initiative you will see the estimated revenue impact in two places.
1. When creating or editing an initiative
The current estimated impact is shown in the top right of the graph. This value is calculated from today until the end of the plan, and calculates the estimated impact you can have with any future changes to the metric.
2. Viewing the initiative in the Initiatives tab
When you expand the initiative in the list you will see 3 values, all of which are calculated from the plan start date.
Importantly, this allows you to see the intended impact of the initiative over the full plan period. Whereas the impact shown when you open the initiative only shows you what could be achieved from today onwards.