I have a duplex and rent half. I enter a total for expenses and allow turbo tax to divide. Shouldn't half my mortgage interest appear on my tax break page?

I have a duplex and rent half.

What do  you do with the other half? Is it your primary residence?

I enter a total for expenses and allow turbo tax to divide.

That's fine. But you have to read the small print on each and every screen. The program does not split everything. It's just not possible.

Shouldn't half my mortgage interest appear on my tax break page?

You'll have to be more specific. There is no screen called "tax break page". So I don't know if you're still looking in the SCH E section of the program, or if you're referring to the "Your Home" section under the Deductions and Credits tab.

Also understand that if you're referring to the SCH A itemized deductions, those only kick in once your itemized deductions exceed your standard deduction. Additionally, there are limits for some items on the SCH A. For example, you are limited to deducting the mortgage interest on the first $750,000 of the outstanding mortgage balance on personal use property (like your primary residence). Interest paid on any amount over $750,000 (SCH A only, not SCH E) is not deductible.

So if the total of your allowed SCH A deductions do not exceed your standard deduction, there's no need for you to have the SCH A at all.