Originally Posted by martin33

Assuming you have a charity in mind, then the issue comes down to basis. For miles earned from employer-paid trips, that's zero (if you were taxed on the receipt of them as income, that income would be your basis). For miles you buy for cash, it would be your cost. For miles you win in a contest, it would presumably be whatever the income value of the prize is. For miles you earn on your own paid trips? Most expert opinion says the basis is zero (effectively treating the miles as a gift from the airline to you; gifted assets inherit the basis of the giver, which is very near zero according to the airlines' financial disclosures). To establish otherwise you would need an ironclad allocation scheme for every ticket (effectively taking the view that every trip is really two transactions: how much of your price is for travel and how much is for "buying miles"), and not even the most aggressive tax advisors have dared dream up such a scheme, nor would the IRS be likely to buy into it.