If I rent only 50% of my primary home, how do I enter the shared expenses, such as property tax, utilities?

[s-abluesky]

If I rent only 50% of my primary home and file a Schedule E, must I calculate the prorated expenses such as utilities?

[Bsch4477]

Yes. And half of your mortgage interest payments and half of your property tax payments will be deducted on Sch A if you itemize and half will be deducted from your rental income. 

[Hal_Al]

It depends on the circumstances of you "renting out" 50% of your primary home?

Roommate  rental

If this is merely a cost sharing arrangement where the amount paid is below fair market rental, there would be no reportable income to you. If the “rent” amount is fair market value, or more, there is still some question as to whether you even have to report it, as it almost always comes out zero. Most people take the attitude that it is not income; it's just room mates sharing expenses and ignore it. Family, as opposed to unrelated roommates, makes that position stronger.

Here’s what you may be required to do:

Report the income (enter at Rents & Royalties/Income & expenses from Rental Properties); and then deduct the expenses on schedule E. If the room mate has full run of the house, and there's just the 2 of you, then half your expenses are deductible (mortgage interest, property taxes, insurance, utilities, repairs, and depreciation [if needed}). Your net income will usually be less than zero.

What you are NOT allowed to do, because it is your own home (you have "personal use") is claim a loss from this activity, to offset other income. Because of the "personal use rule", your deductions are limited to your income. Net effect ZERO.

It is possible for you to gain a positive tax effect from this activity; If enough of your schedule A deductions (mortgage interest &  property tax) are shifted to Schedule E, and your standard deduction becomes bigger than your itemized deductions, you will have effectively saved on taxes.

[Carl]

I rent on 50% of my primary home.

This sounds more like a cost sharing arrangement, than a room or rooms rental. Unless your intent is to make a profit, (usually true if a written agreement is involved) there's really no need to report it at all.