From the merger agreement S-4 at the SEC web link https://www.sec.gov/Archives/edgar/data/64803/000119312518002957/d482402ds4.htm :
Material U.S. Federal Income Tax
Consequences
The
exchange of Aetna common shares for the merger consideration pursuant
to the merger will be a taxable
transaction for U.S. federal income tax purposes. Accordingly, an Aetna
shareholder that is a U.S. holder (as defined in “Aetna Proposal I:
Approval and Adoption of the Merger Agreement and CVS Health Proposal I:
Approval of the Stock
Issuance—Material U.S. Federal Income Tax Consequences”) will recognize
taxable capital gain or loss in an amount equal to the difference, if
any, between (i) the sum of (x) the amount of cash, including cash in
lieu of
fractional shares, received by such U.S. holder in the merger and
(y) the fair market value of the shares of CVS Health common stock
received by such U.S. holder in the merger and (ii) such U.S. holder’s
adjusted tax basis in the
Aetna common shares exchanged therefor.
If a U.S. holder’s holding period in the Aetna common shares surrendered in the merger is greater than one year as of the
date of the merger, the capital gain or loss will be long-term capital gain or loss. Long-term capital gains of certain non-corporate
holders, including individuals, are generally subject to U.S. federal
income tax at preferential rates. The deductibility of a capital loss
recognized in connection with the merger is subject to limitations under
the Code. If a U.S. holder acquired different blocks of Aetna common
shares at different times or
different prices, such U.S. holder must determine its adjusted tax basis
and holding period separately with respect to each block of Aetna
common shares that it holds.
A
U.S. holder’s aggregate tax basis in CVS Health common stock received
in the merger will equal the fair market value of the CVS Health
common stock as of the date of the merger. The holding period of the CVS
Health common stock received in the merger will begin on the day after
the merger.
You can use the average of the 81.65 high and 79.78 low CVS stock price for the FMV.