In this video, we learn how to calculate compound interest. Start with your example of investing $2000 at 3% interest over four years. Now, write down how much you have at the start of year one. To find the percent of this you will need to simply do the amount divided by one hundred and times it by three. Then, you will find the number for the amount of interest you had for that year. Continue to do this for each year and the amount of money you will increase each year. Do this until you reach the fourth year and you're finished!