Now.... If you are not caluclating the interest, but are entering in a amount, it gets easier. You first use the date diff function to calculate the number of days between your start and end date. Then, divide the amount by the result of the date diff calculation. Now you have a amount per day. You next step will be to determine how many days between the start date and the end of that month. Multiply this value by the daily amount. and so on!