Hi @coumbak ! 

You are correct in that your actual expenses such as rent and utilities are prorated as a percent of the size of your home office as compared to the square footage of your entire home. You can also opt to use the Simplified Method, which limits the office space to a 300 square foot maximum, at a rate of $5 per square foot for a maximum deduction of $1500.  However, no matter which method you use, in order to claim your home office as a business expense, that space must be dedicated exclusively to regular business use. The TurboTax program will guide you through entering either actual expenses or the simplified method. Here is a helpful link regarding IRS rules on How Small Business Owners Can Deduct Their Home Office From Their Taxes