Electric and water usage program

Question

 Hello Guys, i would like to make a program to monitor my household water and electric consumption. It doesn't need to be interactive itself with the water and electric meters the user would need to input reading himself after taking them. I would like it to be user friendly so that the wife or any other member of the family would be able to use it.

my idea is to have a window with input fields were the user is asked to enter  water readings, electric readings date readings have been taken and time.(these need to be stored so that calculation can be done ) after the user will continue to enter data.

Obviously the program has to hold meter charges for water and electric meters, rates per units consumed on some amount of units and another rate on some other amount. For both water and electricity.

THE OUTPUT.
This would be ideal to show
 
Previous readings, dates readings were taken (water/electric)
Latest readings, dates readings were taken (water /electric)
Amount of days from previous to latest readings
Give estimate bills for both water and electric separately and total of both
Show meter charges and after include them in total.
Cost per day according to the days between previous and latest readings
Units consumed per day for Water and electricity.

Any idea how to go around this? Thanks in advance