Here are the methods the IRS allows you to use for this situation.
Under the actual expense method, you would need to figure out the percentage of time that the office space was used for each business. Then the usage percentage of each is applied to every home office expense in each separate business. This method would require that you keep accurate records of the time you worked in the home office throughout the year. If you didn’t keep accurate records of the time you worked in the home office, you could consider another reasonable method instead. you must use the same method from year to year,
