Do I have to pay gift tax when I give my adult child a large down payment for a house?

Almost certainly not. The IRS lets you give any one person up to the annual exclusion amount each year with no filing at all; that amount is indexed for inflation and published yearly at irs.gov. Gifts above that don't trigger an immediate tax; they simply reduce your lifetime estate and gift tax exemption, which for most families is in the millions.

If you exceed the annual exclusion to a single recipient, you file Form 709 to report it, but you rarely owe anything. A married couple can each give, doubling the tax-free amount to one child. You can also pay tuition or medical bills directly to the institution with no gift tax consequence at all, on top of the annual exclusion.