In a nutshell - depreciation stops in 2020 on the date you converted the property back to personal use.
When you started renting again in 2022, depreciation starts over from year one, using an "adjusted" cost basis for the structure only. Basically, you have to reduce the cost basis of the structure by the amount of depreciation already taken in prior years. This "could" be more complicated for your situation, since you're talking about a percentage of space in your primary residence. It just depends on how attentive we are to detail and my ability to clearly communicate in a way that does not lead to confusion or misunderstanding.
Also, it's good you're starting this early, becuase there is no way possible you're gonna get done in a day, everything you need to do. I also don't want to give to much information at once, as it can (and most likely would) lead to what I call "information overload". I'll try to avoid that.
I see you have another post concerning capital gains on a house that I presume you sold, in which you had a percentage of business use for a period of time. You really need to stick with one single thread at a time here. I don't care if it's this thread, or the other thread. But I'm only going to respond to this thread. Otherwise, you "will" get conflicting and confusing information if you keep jumping around.
am behind, and have not filed 2020,
Lets start there. But first, you need to confirm beyond any doubt, that the correct amount of depreciation was taken on the 2019 return. My bet is, the depreciation taken on the 2019 return is wrong. This would be due to a program "feature" where a question is worded wrong "for your specific and explicit situation"
On the 2019 return which I presume you saved a copy of in PDF format, you have two form 4562's for the rental. Both of them print in landscape format. One is titled "Depreciation and Amortization Report" and is most commonly the only one you need for this. The other is titled "Alternative Minimum Tax Depreciation", and you may not need it. But print that one out also in case you're asked for AMT information later.
On that first 4562 you'll have an entry for the rental portion of your house. I'm expecting the column for "prior years depr" to be blank, and for there to be a figure in the "current year depr" column. That's the figure we need to confirm is correct, as I'm betting it's flat out wrong. Please, prove I'm wrong on that assumption.
To confirm if I'm right or wrong, see IRS Publication 946 at https://www.irs.gov/pub/irs-pdf/p946.pdf and use the MACRS worksheet that starts on page 37 of that document. For item #6 on that worksheet, you'll use table A-6 on page 72 of that document.
If you confirm the amount on the 2019 form 4562 is correct, then we'll continue with the 2020 tax return, since you've not started it yet.
If you confirm the amount on the 2019 form 4562 is wrong (I fully expect it to be wrong) I"ll help you with amending the 2019 return to fix this. Then you can started your 2020 return ensuring you import data from the amended 2019 return, and not the original return.
