The first thing you must do is estimate the amount of time that you spend in the office for the various uses, i.e., spent on K-1 business, LLC business and rentals or whatever applies. Then separate the square footage used based on the percentage of total for each business. For example you use the office 56% for K-1 and 44% for the LLC or whatever applies. Then this expense has to be listed on the Schedule C for each business. That means that information must be listed separately for each business. If any major modifications are made for the office, this must be added to the cost that you are using to write off the square footage. (First compute the cost of the room based on the square footage of the office space as a percentage of the square footage of the entire home, and then add the modifications that that number. You MUST keep tract of all your computations that you make for square footage, usage, etc because when you are audited you will need to furnish this information to the IRS. As a general rule, if you deduct a home office your chances of being audited increases dramatically. If you need the deduction then compute it and use it. But if you don't or it makes a little difference then don't bother using the home office deduction.
