Let's say I go to a CPA for this tax year 2019. I can go back using TT after that?
Sure you can. But make *ABSOLUTELY CERTAIN* that you get a printout of the "complete" tax return *AND* all worksheets and calculation forms from the CPA. *you* *WILL* *need* *them*. I guarantee it.
It should be the same number for the depreciation.
No, it will *NOT* be the same number for depreciation. Won't even be close. Again, I can guarantee it with 100% certainty. You may or may not be paying back-taxes (I think not) but you will be paying some penalties and fines for not having taken the depreciation when you should have. So there's no way possible the depreciation amount for 2019 will be anywhere close to what it will be for 2020.
Since you can amend a tax return for three years back, a CPA will probably amend the 2016 tax return with the 3115 to "correct" your mistake. Then amend the 2017 and 2018 returns to correctly take the depreciation. Then (and only then) would the amount of depreciation for 2019 be the same (or within a few dollars) of the 2018 depreciation.
You need to get on this yesterday if not sooner. Since you can only amend a tax return 3 years after you filed it, assuming you waited until the last minute to file your 2016, your deadline is approaching. Keep in mind too that already CPA appointments are filling up fast as I type this.
