Let me clear it up. Even though the correct mathematical formula is:
ROI = (gain from investment - initial investment) / initial investment * 100 %, I will clear it up with words:
Obviously, there are two interpretations of return on investment here. Return as in whatever you get back from your investment (the OP's definition), and return as in the profit you get from it.
When you are to consider what the ROI is, there are some elements you need to consider:
The element which is missing explicitly in this discussion is the specification of the last element in the list above. For example, using the OP's example, when the intitially $100 invested is withdrawn from the AdWords account, there is no equity left in his AdWords account. Thus, there is no equity left in the object in which one initially invested the $100 in. The only parts left to consider are $100 which was the intial investment and the $100 which are revenues. 100 in and 100 out, equals to zero which is a 0 % ROI.
Another example is if one buys a $100 stock and receives a $100 dividend, and one can sell the stock again. Taking this into consideration, the ROI so far on the stock is 100% because we have three relevant elements to consider:
Basically, the OP fails and the ROI in his example is 0%, not 100%.
ROI = (gain from investment - initial investment) / initial investment * 100 %, I will clear it up with words:
Obviously, there are two interpretations of return on investment here. Return as in whatever you get back from your investment (the OP's definition), and return as in the profit you get from it.
When you are to consider what the ROI is, there are some elements you need to consider:
- The initial investment
- Inflow from the investment - revenues, dividends etc
- If there is equity left; also depending on whether one has sold the asset in which one first invested or not, and if one sold, what the sales price was
The element which is missing explicitly in this discussion is the specification of the last element in the list above. For example, using the OP's example, when the intitially $100 invested is withdrawn from the AdWords account, there is no equity left in his AdWords account. Thus, there is no equity left in the object in which one initially invested the $100 in. The only parts left to consider are $100 which was the intial investment and the $100 which are revenues. 100 in and 100 out, equals to zero which is a 0 % ROI.
Another example is if one buys a $100 stock and receives a $100 dividend, and one can sell the stock again. Taking this into consideration, the ROI so far on the stock is 100% because we have three relevant elements to consider:
- Initial investment of $100
- Dividends $100
- We can sell the stock - whatever the price is atm doesn't matter, since in my example the stock hasn't been sold again so we don't need to take the sales price into consideration, but we must consider that there is still equity!
Basically, the OP fails and the ROI in his example is 0%, not 100%.