To calculate percent change you have to take the first value and subtract the value you have now. Then divide by the total value and multiply by 100. So if you had 12 apples at the beginning of the day and 8 apples at the end of the day you would subtract 8 from 12. (12 minus 8 equals 4) Then you divide 4 by your first value which is 12 (4 divided by 12 equals 0.33). Then you multiply by 100 (.33 .