You're right that TT has calculated the depreciation each year, by asset, and "knows" the cumulative depreciation. However, last year I found that in the TT step-by-step process, it determined the allocation of the sales price and cost basis of the assets for the "business portion" for purposes of completing Form 4797 - Sale of Business Property - using the business-use-percentage in the last year (i.e. year of sale). Since my final year had a far different business-personal ratio than in prior years (in fact every year was different) I concluded this was incorrect -- You have probably noticed each year that as the business use % changes, so does the depreciable cost basis amount and therefore the depreciation deduction even if using straight line. So I developed an historical weighted average of business versus personal use which I then used to allocate the sales price and cost basis of each asset. This required me to use the "Form" view in TT and to override cell amounts for each asset in Part III of Form 4797 for lines 20 (gross sales price) and 21 (Cost or other basis). Note that line 22 (Depreciation) should come straight from the TT accumulated depreciation calculations you referred to; these do not and should not be overridden. You then should get a reasonable allocation of the gain on sale between the business and personal portions for purposes of Form 4797 and Schedule D. I would also recommend that you complete IRS Publication 523, worksheet 2 - "How to Figure Your Gain or Loss" for both the business portion and the personal portion of the asset you sold, using the same historical weighted average of business versus personal use I referred to above.
Please note that I am not an expert and what I described above is something I figured out after playing around for hours with TT to get something that made logical sense.
