You can use Microsoft Excel software (or something equivalent) and set up a spreadsheet with individual columns for the 12 months of each year and rows for the monthly cost and monthly usage. Then program the spreadsheet to sum the columns across. Each month, when you receive a bill from your utility company, add that month's cost and usage and update the spreadsheet totals. If you prefer to do these calculations without a computer, set up the spreadsheet the same way on a sheet of paper. Then you'll just need to do the math by hand or with a calculator.
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