You can choose any 12-month period for your medical expense claim, as long as the period ends in the current tax year. For example, the earliest possible claim period for the current tax year is January 2, 2020, to January 1, 2021. With this claim period, the oldest medical expense you can claim on your 2021 return is an expense from January 2, 2020.
After you enter your medical expenses, TurboTax prompts you to set your claim period. You can use a different 12-month period each year; your 12-month period doesn’t have to start where your previous 12-month period ended. However, you cannot claim the same expense more than once.
For more information please refer to TurboTax FAQ:
Can I claim prior year medical expenses?
Thank you for choosing TurboTax.
Yes, you can claim premiums paid to a private medical plan in 2020.
In order to do this check the last box on the "your medical profile for 2021" page, you will select Private Medical Plans and Quebec Perscription Drug Insurance Plan Premiums for 2020.
For more information please refer to the following TurboTax article: