Correct, if you are using the actual expenses method, it will take the home office use % (which is based on square footage) and apply it against your total utilities. Just make sure you enter it in the correct column (for entire home) as there is the option for entering utility amounts solely attributable to the home office space.
The simplified method for home office deduction is $5 per square foot (if 12 months use) and therefore will be limited based on one month use. It is advisable to try both and see which gives you a better deduction. With this method you won't have to enter any utility costs, etc.
