Home office deduction: For "entire home" actual expenses for home office that existed only part of the year, does TurboTax want me to enter the entire year's expenses?

[pher]

One of the first questions TurboTax asks when starting the home office deduction: "In 2022, how many months did X use this office at least 15 days?" TurboTax says it'll use this to determine how many months actually qualify for the home office deduction.

Let's say the home office didn't exist (business didn't start) until September, and so the answer to the above question is 4 months -- Sept through Dec (a third of the year). When entering subsequent "entire home" expenses using the "actual expenses" method, TurboTax asks for things like real estate taxes, utilities, repairs, etc.

Is TurboTax wanting me to enter *the entire year's worth of expenses* and it'll then divide by 3  (since the office was only used for 4 out of 12 months) for each of the values before it puts it into Form 8829?

Originally, when I was entering real estate taxes and things that have a yearly cost, I thought TurboTax was asking me to enter the entire-year cost (assuming it would divide). But then when I got to repairs and utilities, I realized that this can significantly vary from month to month (for example, a repair in March wouldn't qualify since it was before the home office started in September -- but a repair in October would qualify). And another example is that utilities can be significantly higher in fall/winter months at the end of the year, compared to earlier in the year (in which case, simply dividing the entire year's costs by 3 would be under-deducting).

I could enter a third of the taxes myself (i.e., those that represent Sep - Dec), and enter just the Sep - Dec utilities and repairs etc., but then I'm worried that TurboTax may actually divide this amount by 3 again. That of course would be significantly under-deducting. (If that's what TurboTax does, then perhaps I could simply multiply my Sep - Dec expenses by 3, knowing that TurboTax will divide by 3, and I'll end up with the correct result -- but of course I shouldn't do that unless that's what TurboTax is actually going to do, or I'll end up over-deducting.

Side note: I do understand that TurboTax will prorate the expenses based on the percentage of the home (sq ft) that was used as a home office. But it's unclear to me whether that TurboTax proration also automatically incorporates the number of months that qualified, or if I'm supposed to do that myself before entering values.

[pher · Accepted solution]

Self-answer: Enter just the portion related to those actual months. TurboTax won't actually divide (so I'm not sure why it asks the question in the beginning).

I figured it out because I just now noticed hyperlinks at the bottom of these pages, which say:

"How do I enter my mortgage interest if the time I used the office and the time I paid mortgage interest are not the same?"

"Didn't have the office for all the months I paid expenses in this home?"

For example, the answer to the second question says the following:

"Since the time you lived in your home and the time you had your home office are not the same, enter expenses only for the time you used the space as a home office, not for the entire time you lived there.

For example, if you lived in your home all year but didn't have a qualified home office until August 1, and then had the office the rest of the year, enter expenses you had from August 1 to December 31.

Your expenses for the time you didn't have the office are considered personal expenses and are not deductible."