All utility bills may have fluctuations because there are so many variables from one year to the next. For example, if you have a natural gas water heater, range and clothes dryer you would have to have the exact same usage. That would mean exactly the same number of showers for the same length of time. You would have to cook the same length and number of times and you would have to do the same amount of laundry.
If there is a significant fluctuation we can do a free energy check-up to try and see what is taking place. This is a great question. Thank you for submitting it.