For some years I have operated a home office, and taken the home office deduction. The home office deduction (at least prior to the introduction of the simplified method) mandates calculating depreciation on the property, and later recapture of this amount if the property is sold.
I took the original purchase price minus land, and have set up a MACRS SL depreciation table over 39 years. I deduct the percentage attributable to my home office (here 10.9%). So far so good.
Now I've completed an addition to the home, so set up a second 39 year MACRS SL table for the addition. Here's where I get into trouble. Where on Form 8829 would I enter this data? Line 36 is no good, as that won't reflect the different starting dates for the depreciation.
TurboTax is no help, creating crazy numbers:
(Above I temporarily set the value of the addition to $9,000,000 to see where the values where flowing to. Note the whopping calculation error.).
So how do I report home office depreciation, consisting of contributions from two or more parts of the home, each with their own depreciation start date?