The idea of computation is not very clear. As I understand, if you want to show the estimated percentage of sales for today, then the calculations should be based on the formula
=Week(Today())/52 (share, if in percentage, need multiply by 100.
More accurate calculations make sense, because it's still a forecast).
If the forecast is based on selection, then today date does not play any role and it is necessary to calculate a maximal week of selection, like this
=If(GetSelectedCount([FieldDate])>0, Week(Max([FieldDate])))/52 (in year 52 weeks).
I'm sorry if I'm wrong. Maybe I just did not understand your idea.
Thank you for the quick repose!
It's not necessarily a forecast, more of a reference figure to show how much of last years total sales we could have excepted to already achieve. Week(today)/52 shows the current percentage of the year we have covered, but I would prefer if when for example I selected the first 10 weeks of the year, it showed the target to be 100% because we have covered all of those first 10 weeks. If I have selected weeks 15-30, it should show 37.5% because we are in week 20 and have covered 6/16 weeks in the aforementioned range.
Does that make sense?
Sorry for the confusion!