You don't declare any amount. The program does that for you based on the data you enter. Some of the things that matter are the square footage of space that is "exclusive" to the renter, and number of months that space was "in service" as such. You should be working this through the Rental Income & Expenses (SCH E) section of the program. On one of the screens near the beginning of that section, make sure you selected the option for "I rent out part of my home" and work it through from there. The program figures your allowed depreciation based on that, and other things too, such as your MAGI and the such.
Understand also that the rental space you are declaring (25% seems a bit high to me) is that space that is "exclusive" to the renter. None of the common area counts. For example, if you live in a 2BR/2BA house, where you occupy the master bedroom and the master bath is only accessible from that bedroom, then obviously that's not rental space.
But if the 2nd bath is across the hallway from the room that you are renting out, that 2nd bath is not "exclusive" to the renter. It's accessible by your guests visiting you for example. So the floor space of that 2nd bath can not be included in your percentage of rental space.
