Can i deduct the full cost of an online course on my schedule c

[MaryK4]

It depends- to be deductible, a business expense must be both ordinary and necessary. An ordinary expense is one that is common and accepted in your industry. A necessary expense is one that is helpful and appropriate for your trade or business. An expense does not have to be indispensable to be considered necessary.

If you can show that the course truly helped your business you can deduct it.  Also, if the course is part of a degree program it will get additional scrutiny.  Be wary if your business is not showing a profit- you must be ready to defend the deduction if you are audited.