How to add horizontal line to chart?

Inserting a horizontal line to a chart is very possible. But, first we need a chart that looks like this:

data table

1. Add a new label to the data (1), and click on the cell under it to type =average(all the data with value) (2).

average formula

Note: This step is just a possible way to inform Excel what information to use for the line. You should repeat this step on all the remaining cells to match the rows of the remaining columns.

2. Right click on any of the series, and choose select data.

select data

3. Click add

add series

4. Choose the cell for series' name (1), and cells for the values (2). Then click ok.

series name

5. Press ok again.

6. Right click on any of the average series (1), and choose change chart (2).

change series chart type

7. On the chart type, change the chart to line. Now, click ok.

change to line chart

The final result would look something like this:

horizontal line chart example