If you are a non-QC resident > You can't do this claim.
Both spouses have to claim the same 12 months window. Box 85 on the T4, is a 12-month window usually from Jan 1st to Dec 31st. So, if you claim one year in one return, you cannot claim the other year in another return. You can start the expenses claim at any month in 2018, but the last month has to end in 2019.
The software claims whether your medical expenses are high enough to claim or not. Your total expenses for 2019 need to be more than 3% of your net income or more than $2352 whichever is less.
If you are a QC resident:
You can claim the 2018 premium in the Federal return and end the medical period in the taxation year, and claim the 2019 premium in the Quebec return.
I hope this was helpful
