For most investors the Return on Investment (ROI) is equal to the resulting amount divided by the initial amount. Investors usually express this fraction as a yearly percentage. Usually this percentage is compared with the ROI on other investments, such as a savings account.
For the ROI of extremely short term investments such as with day-trading a number of other aspects are important as well. The ROI should not be compared with the ROI of a savings account. Instead the aimed for ROI on this kind of investments should be much higher than the ROI on long term investments since the risks are much higher. In addition transaction costs, currency fluctuations and the costs of trade debts are often significant and need to be taken into account.