Percent summary in Excel

A simple question -
A yield table includes the calculation of yields each month.
Let's say in the first month of investment I write 0%
In the second - 1%
And in the third month - 1.5%

This table has a graph of a line.
The problem: In the third month the graph is 1.5% and the percentage was not agreed (the answer was 2.5%)
So how can this problem be solved.

Thanks in advance,

Sorry for the mistake if there is.
I do not know English well and uses Google Translator.

The result of Month 2 was an addition of 1.5%
But I'm interested that the graph will not show it to me but the total amount of results.
Ie Month 2 (1%) + Month 3 (1.5%) = 2.5%

sorry !

The result of Month 3 was an addition of 1.5%
But I'm interested that the graph will not show it to me but the total amount of results.
Ie Month 2 (1%) + Month 3 (1.5%) = 2.5%

I think that's the story.

I understand that in the data table I have to type in the value of the month not the value of its change
But something like -
= D3 + 1%
The question is how to do it automatically - that I can simply type in the data for the month itself. And get the general summary?

I really thank you for your help.
Attached is the file on which I work. (I hope I got it right)

The theme of the file is tracking several investment tracks.

These are two worksheets -
1. The Investment Results Table by Months (from 6/17 - 5/18)
2. Graph of results.

The point is that if I write in the table the result of that month - it appears in the graph regardless of the previous result and not in the continuation graph.

I tried to make two columns -
Column 1 of the results of that month.
And column 2 of the summary of the results up to that month. (When the graph takes its data from column 2)

The problem was that the table and automatically the graph also show the results of the months that have not yet been. Because their slot in column number two already includes the sum of the months ahead.

I hope I have been able to explain myself well.
Thanks again for all your help.