According to a document on Abbott's website, one approach acceptable to the IRS is is to allocate the original cost of the original Abbott shares between the ABT and ABBV shares according to their fair market value as of Jan 1 2013. Their numbers:
1. 47.9751% to Abbott common shares .(US$ 32.045 / (US$ 32.045 + US$
2. 52.0249% to shares of AbbVie common stock (US$ 34.75 / (US$ 32.045 +
I can't believe that the IRS doesn't have a firm formula for this calculation. AbbVie's document says there are a number of ways to define the value of ABT and ABBV on the first day of trading and you should consult your tax advisor. You can use the opening trades, the closing trades, the average of the two or any other definition you can justify. That's crazy. Define one method and be done. The example they use is the average cost and they show ratios of 47.9751% for ABT and 52.0429% for ABBV. Take your old cost basis fro ABT and multiply by the above percentages and that's your new cost basis for each.