How to implement countdowns on the balance of funds in the form of a graph?

Question

Android

Good day to all.
I have a DB where the user enters data on monthly income and expenses for each type of expense/income.

(That is, for each type of "product", the user enters expenses and income for the month. Let's say that the user is studying under a contract and is also engaged in tutoring, hence Accommodation income: 7000 and coast:11000)
And I need to make a countdown in the form of a graph.
And the schedule itself must be done exactly according to the balance of funds ( coast - income ), i.e. something like this:

For this, as I understand it, you need to use GraphView:

...
 <com.jjoe64.graphview.GraphView
        android:id="@+id/graphF"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
...

public class GraphicsFunctionActivity extends AppCompatActivity {

    private LineGraphSeries<DataPoint> lineGraphSeries;
    private GraphView graphView;
    private double globalRemainder = 0;
    private double coast = 0, income = 0, time = 0; // Система координат (x;y), где x - это прибыль coast - income, y - время


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_graphics_function);

        graphView = (GraphView) findViewById(R.id.graphF);
        lineGraphSeries = new LineGraphSeries<DataPoint>();
        update();
    }

   private void update() {
     // ?
    }

   }
}

All the necessary data (namely coast and income) I can pull out from SQLite using HashMap. And then calculate the total balance of each individual product (in foreach execute int remainder += coast - income). But I don't know how best to do it.