What is the federal excise tax on charter flights?

The FET applies to domestic commercial air transportation, which charter is. It's calculated on the amount paid for the flight; on our sample coast-to-coast itemization it's the $3,300 line on a $47,260 trip. International flights are structured differently (segment fees and international facility charges rather than the 7.5%), which your quote itemizes when it applies.

The practical use of knowing this: it's a fast honesty test for quotes. Any domestic quote should carry the line, computed and visible. If it appears only after you commit, ask what else does.