Budgeting for utilities can be frustrating, especially in places that have 4 distinct seasons. The increase in winter bills comes when many are also paying for holiday gifts. In our case it's also when my husband's checks take a 2-3 month nosedive. I also wanted a better handle on how much money it takes to run our household month to month.
Last spring I set a utility escrow sub account at ING to help work in this problem. I pulled our last 7 bills (we'd only live in the house 7 months) and did some math to figure out what our average would be. If you have all 12 months just add them up and divide by 12. I was missing spring/summer months, so I took the one summer month I had, multiplied it by 6 and then added the winter month and divided it all by 12. Based on our apartment bills and our lack of AC use I knew that the spring/summer months would be about the same.
To automate the process I added a formula to our spending spreadsheet in Excel. It's set up to take our annual number ($125) and subtract the monthly bill amount that I was already plugging in. At least once a month I spend a few minutes transferring money to/from ING, so this transfer just got added to the mix. Once our bills exceed the annual average I'll pull the money we've been setting aside to pay the difference.