I will fly into France from the U.S. with my personal laptop. I also want to take a new one as a gift for my hostess.
Will I have to pay a tax duty on it?
Yes, you'll be liable to pay 20% VAT on a new laptop if its value is greater than €430 euro in to France from outside the EU customs area. On the plus side, there's no specific duty to pay (see "Ordinateur portable" on this page)
You could try and just walk through the "nothing to declare" aisle anyway - but you'd then be smuggling and at some risk of facing penalties.
Before bringing a laptop from the USA as a present, consider that it has the wrong keyboard, the wrong power plug, you need to make sure that it works with 220 Volt, the receiver may have a hard time getting warranty repairs, and the receiver will not have any EU consumer rights.