Whether your income exceeded the credit allowable for your health insurance premium is calculated by the year, not by the month.
Your problem is one of the issues with the way the current bill is written. When people have a major change in their lives - going from single to married, from being unemployed to having that dream job, or just getting a better job with a higher salary - they can find themselves having to pay back a significant chunk of the Advance Premium Tax Credit that they got before this life change happened.
The reason that TurboTax does not provide the opportunity to calculate your income for the months that you had insurance is because the IRS would ignore that information. They only look at your total income for the year.
