@danielle-51
"de minimis" is a latin (fancy legal) term for "minimal." If you routinely use the computer for both personal and business use, you should allocate the percentage based on some method of determining use, for instance if the computer and printer is used 20% for personal, then only 80% of the cost is a business cost. However, if the personal use is rare, occasional and minimal, then you can ignore it.
I can't find a strict number, but I recall this example from a discussion about the home office deduction. Suppose you use a spare bedroom as a home office and you meet the exclusivity rule, the bedroom is only ever used for business. But, you have personal items stored in the closet, and you must occasionally enter the office to access the closet. While this is a "non-business" use of the home office (walking across the floor to get to the closet), it is also considered de minimis, or so minor that the IRS doesn't care.
