Line Chart with Starting Point and Variable Monthly Values

Dear All,

I am currently struggling to create a line chart that shows the following:

I have a starting value of 10.000 EUR. Every month new actuals will be uploaded and they vary (see example in table below). Instead of showing the actuals in a line chart (which I was able to do), I want to show the values in the column "Starting Value". However, I am not sure how to calculate this in Power BI, so it automatically takes the new starting value every month and reduces it by the current actuals.

I hope it is clear, what I mean. If not, please let me know. 

Thank you very much in advance for your support. It is much appreciated.

Best regards,
Kathi