Opening the dataset. We need to create a calculated field first
Calculated Field: Monthly Position Calculation
IF [Description] = "Gained" Then DATETRUNC('month', [Date]) + 5
ELSE DATETRUNC('month', [Date]) + 10
Right-click and drag calculated field to Columns and select continuous Month. Drag Computed Net to Rows, change Marks card to Gantt Bar. You will have following canvas.
Click the drop-down arrow on Monthly Position Calculation on Columns and select Exact date . Create second calculated field:
Calculated Field: -Amount
Drag -Amount to Size and Description to Color. You will now have a waterfall chart
2. Discreet Chart
If you want to compare monthly gain and loss with a much easier look. Here is a trick you can do. Drag Description to Columns, remove Monthly Calculation Position. Move to Date to Columns as well, select discreet Month.
Feel free to filter division if needed and now you will have a discreet waterfall chart.