You use the same ratios for the sales price and cost of sale that you used when you put the assets into service ... it is a simple math problem using ratios ... don't dive deeper into the pool than that. If you have NOT entered and depreciated the assets over the years it was a rental then RUN to a local tax pro to get this massive error corrected.
A simple example of ratios ... if you have more assets than the example then you will have more lines. Remember if you divide a big number into a littler number you get a % ... thus 5000/100,000 = 5%
original cost basis ratios Sales price cost of sale
home 80000 80% 160,000 8,000
land 15000 15% 30,000 1,500
Imp 5000 5% 10,000 500
totals 100,000 100% 200,000 10,000
All you need to enter into the program is the % of sales price & % of cost of sale for each asset ... once you have these figures the entry in the asset section is simple.
