Waterfall Chart with offset

I'm trying to use the waterfall chart to see how I'm doing in my "Planned" costs.

My problem is that if I want to see my 2018 performance per month it wouldn't show me how much I "Currently" have.

Let's say that I'm starting off with 100,000$ which I had accumulated in 2017.
Then in 2018 I started losing 20$ monthly until June (6 months). When I show the waterfall chart in 2018 it will show that my total is -120,000$ (-20,000 in 6 months) however that is not true because I'm starting off with 100,000$ so the total should be (-20,000$) only.

Is there a parameter that I can set of how much is my starting amount?