Which of the following is required for home-office expense deductions?

The requirement that the office must be within the taxpayer's primary residence is crucial for claiming home-office expense deductions. This is based on IRS criteria that designate where the home office is located. For the expenses to be deductible, the workspace must be part of the taxpayer's main home. This ensures that the deductions are appropriately associated with a legitimate business use of the home, rather than just a casual or infrequent use of space in a living environment.

The remaining options suggest various conditions regarding size, frequency of use, and financial practices that are not required for home-office deductions. There is no stipulation regarding the office having to exceed any specific size, nor is there a minimum requirement for the number of days worked in that space. Additionally, while maintaining a separate business account can help in tracking expenses, it is not a requirement for the home-office deduction itself. Therefore, the correct focus is solely on the requirement that the office be part of the taxpayer's primary residence.