Can my wife deduct the cost of furniture (guest chair) for the room in our house she uses when she teaches voice lessons?

[Marketstar]

How much did you pay for the chair?

[viktoriyab11]

Yes, she can deduct percentage used for business. Office furniture, being necessary for the business, is treated as a business expense. This expense is deductible on your tax return. 

You must deduct only the amount you spend on furniture used as part of your business.

The deduction would be either depreciated over many years, or you may take a section 179 deduction to deduct all or a portion of your furniture in the year you purchase it. 

Anything purchased for less than $200 can be deducted in one year.

The items costing more than $200 and less than $500 if you attach a statement to your tax return indicating that you are electing to use this rule, deductible in one year.

Reporting Self-Employment Business Income and Deductions https://turbotax.intuit.com/tax-tips/self-employment-taxes/reporting-self-employment-business-income...