Do you know why I have to include the cost basis of a stock donation to a charity? I'm entitled to the fair market value on the day of the donation, so why the question?

Why am I asked for the cost basis of a stock donated to a charity and held for over a year when using the turbo tax program?  I'm entitled to the fair market value on the day I donate it.  What do I put in the box to assure I get the FMV I'm entitled to?