Last year's medical expense claim period was Jan 1 to Dec 31. This year can I use Jan 1 to July 31 (6 mths) so that I can use the remainder of expenses next year?

Yes, you can claim your medical expenses from the first 7 months (January 1 to July 31) and claim the remaining in the next year. 

Unlike most other expenses, medical expenses don’t have to follow a calendar year. You are allowed to pick your 12 month period. As long as the end of the 12 months falls within the tax year you are reporting, you are free to choose the best time frame for your situation. Let’s say you had a ton of medical expenses from November until March. Both kids got braces, your spouse spent a bundle on glasses, and you had to have some physiotherapy due to a fall. If you choose to follow the calendar year, you might be shorting yourself some cash. The 3% rule will be applied to the expenses in two different tax years. If you make your twelve month period from November 1 until October 31, you’ll be able to lump all of these expenses together on your return that October falls into. This maximizes the impact as the total will only be subjected to the three percent rule once. If you choose to alter your twelve month period, make sure you keep track of the dates for future years.

As seen in this Canada Revenue Agency (CRA) link: Details of medical expenses

Prescription drugs and medications that can lawfully be obtained for use by the person only if prescribed by a medical practitioner. Also, the drugs or medications must be recorded by a pharmacist. You cannot claim over-the-counter medications, vitamins, or supplements, even if prescribed by a medical practitioner (except Vitamin B12). 

For more information please see our TurboTax FAQ: 

How do I choose a claim period for medical expenses?

3 Tips For Claiming your Medical Expenses as a Tax Deduction

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