Once your initiative progresses to the L3 stage, the Impact Plan line will lock down and will no longer be editable. You will see two new rows for entering Actual and Forecast values.
Forecast (sometimes called 'Revised') is meant to serve as an updated estimate of the originally defined plan. Wave will only allow forecast values to be entered for current and future months.
Actual impacts are entered once your initiative has made it to L4, which is when you switch focus from implementation toward realizing value. Actual impacts can usually only be updated for the current month and previous month; your instance of Wave may have a slightly different configuration
Please note that some configurations of Wave only allow Finance Team members to enter actual numbers. Others allow initiative owners to enter the actuals and then the Finance Team later validates the numbers that have been entered.
Note: If your initiative is in L3, L4 or L5, and you need to modify values in the planned series, you either need to:
Update the initiative back to the L2 stage and resubmit for L3 approval.
Talk to your company's Wave representative or work stream lead to manually update the value/s.