The first thing you need to be aware of is that it depends on whether you used the actual expense home office method or the simplified home office method. If you used the method in TurboTax where you just enter square footage and it calculates a deduction based on that, then you are using the simplified home office method, which doesn't allow you to additionally add other home office expenses like furniture. If you did use the simplified home office method on a previously filed tax return, you cannot change that election retroactively, so in that case you are stuck with that for that tax year.
If you are using the actual expense method, then you can add expenses for your home office for things like furniture. TurboTax won't automatically claim the past depreciation for the past years because you can only claim the current year's depreciation. You can use form 3115 to claim past missed depreciation. However, form 3115 if a complicated form with additional required attachments you need to add to it, and it's unlikely to be worth the time and/or expense to go through that process to claim past home office furniture. You do have the option to file an amended return to claim missed depreciation for only the previous tax year (you can't go back more years than 1 to claim past missed depreciation).
One other caveat to be aware of is that you can only claim a deduction for the home office if the associated business has a taxable net profit for the current tax year. So if it's a home office for a rental property, for example, with negative taxable income for the year, then the home office deduction wouldn't reduce your current year taxes anyway.
David O
