Bar chart with actual margin to date then forecast margin

[Anonymous]

I'm probably making this more complicated than it needs to be but I can't see it anywhere. I'm trying to produce a chart for the year that uses actual figures until the selected month and then the forecast beyond that to year end. The expression I have a the moment is:

                        =If(????,Only({<Month>}MarginForecast),Only({<Month>}KPIMargin))

And I'm struggling with what to put in the If statement.

The data looks like this (dummy data):

MonthYear	Total Stream Revenue Planned	Total Stream Revenue Forecast	Total Stream Revenue Reforecast	Total Stream Revenue Actual	Total Stream Costs Planned	Total Stream Costs Forecast	Total Stream Costs Reforecast	Total Stream Costs
Jan-18	500	500	500	450	400	400	400	423
Feb-18	500	500	400	400	400	400	400	497
Mar-18	500	500	500	350	400	400	400	400
Apr-18	500	400	400		400	200	400
May-18	500	400	400		400	200	200
Jun-18	500	450	450		400	200	200
Jul-18	500	300	300		400	200	200
Aug-18	500	300	300		400	200	200
Sep-18	500	300	300		400	200	200
Oct-18	500	300	300		400	200	200
Nov-18	500	300	300		400	200	200
Dec-18	500	300	300		400	200	200

The relevant bit of the script is:

[Total Stream Revenue Planned] - [Total Stream Costs Planned] as MarginPlanned,

[Total Stream Revenue Forecast]-[Total Stream Costs Forecast] as MarginForecast,
[Total Stream Revenue Reforecast]-[Total Stream Costs Reforecast] as MarginReforecast,
[Total Stream Revenue Actual]-[Total Stream Costs] as KPIMargin,
[Total Stream Revenue Actual] as Revenue,
[Total Stream Revenue Planned] as RevenuePlanned,
[Total Stream Revenue Forecast] as RevenueForecast,
[Total Stream Revenue Reforecast] as RevenueReforecast,
[Total Stream Costs] as Costs,
[Total Stream Costs Planned] as CostsPlanned,
[Total Stream Costs Forecast] as CostsForecast,
[Total Stream Costs Reforecast] as CostsReforecast,

If a month is selected I get:

I can get this with no month selected (which is what I want it to look like), but it messes up 17 other items on the dashboard:

Does anyone have any ideas?

Thank you