Be aware you deal with two percentages when renting out a part of your residence. Percentage of floor space and percentage of time.
The screenshot provided earlier is asking for percentage of floor space. The percentage you enter here is for the floor space that is exclusive to the renter and typically does not include common areas shared with the owner. Typically this will be less than 100%.
Percentage of time is for the time the space exclusive to the renter it was used as a rental, starting from the date it was placed in service. This will almost always be 100%. The only way it's less than 100% business use is if the owner used it for any personal reasons *after* the date it was converted to rental. What that space was used for before it was converted, doesn't count for anything.
Finally, double-check the depreciation amount, as I expect it will be wrong. In IRS Pub 946 at https://www.irs.gov/pub/irs-pdf/p946.pdf use the worksheet on page 36, and for line 6 of that worksheet table A-6 on page 71 is used.
