How do I allocate insurance premium percentage for a shared plan?

If you're referring to a shared 1095-A, both you and the other person need to enter a copy of the Form 1095-A that you received on your tax returns. TurboTax will ask you questions about if the policy was shared with someone and how to allocate the costs and credit. 

1. Login to TurboTax 
2. Select Federal  and Deductions & Credits
3. Scroll down to Medical and select Show More
4. Select Start/Revisit next to Affordable Care Act (Form 1095-A)
5. Answer yes, I received Form 1095-A
6. Enter the information and select Continue
7. Select I shared this policy with another taxpayer who’s not on my taxes and Continue
8. On the next screen you will enter the SSN for the other person and the start and end months that you shared the policy with the other person
9. You will also choose the percentages of the amounts you want to claim on your tax return.   Both percentages should add up to 100%
10. TurboTax will calculate the information that should be on your return based on your answer