How are presidential vetos overriden?

Answer Yes, it requires a two-thirds majority in each house of congress.

It's almost impossible to do, because of the two-thirds majority it requires.

You'll hear of bills that passed with veto-proof majorities. These are very rare today. A bill that passed with a veto-proof majority is one so popular more than two-thirds of each house voted to approve it. Which, of course, means the bill contains spending for each Member's district. These rare bills are normally signed by the President because Presidents hate having vetoes overturned.