You will see an option when you first set up the property to let TurboTax do the math to enter your indirect expenses to allocate them to non-business use as follows:
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Thanks. I think I did that last year, but I used TurboTax Home and Business 2019. This year I tried using TurboTax Premier online and it doesn't seem to be doing the calculation for me, it asks me to enter a number for this.