Excel chart: How to reverse the X axis of time series data

"Click the axis for the categories, values, or series whose
plotting order you want to change.
On the Format menu, click Selected Axis, and then click the
Scale tab.

Note Selected Axis is only available on the Format menu when a
data series is selected.
To reverse the plotting order, do one of the following:


For categories, select the Categories in reverse order check box.
For values, select the Values in reverse order check box.
For series in 3-D charts, select the Series in reverse order
check box.



[Source]"

"SJohnny, similar to you, I had some financial data displayed with dates on the Y axis, and I had the same problem; the line graph I created initially was backward. However, without using an XY graph, there's a simple way of fixing the chronological order of the data.

Select the data you want to graph.
Using the graph function (Chart Wizard), select a line graph.
At step 3 of 4, under ""primary axis,"" select ""Time Scale."" This should immediately correct the order for preview before you finsh creating the graph."