How many years did the Hundred Years’ War actually last?

How to get close to this number

This is a question about a name, and the name is the trap. Any figure that appears in the title of a historical event is a label applied afterwards, usually rounded, and almost never the measured duration. The moment you notice that the question is asking "actually", you should expect the answer to differ from the hundred in the name — and the only question left is in which direction.

It went longer, not shorter, which surprises people who assume labels round down. The war is conventionally dated by the opening claim and the final expulsion, and those bookends sit more than a century apart. Historians picked a memorable round number for a conflict whose real boundaries are messy, which is what naming conventions almost always do.

The deeper caveat is in the explanation: it was not one war. It was a series of campaigns separated by truces long enough that people lived and died entirely within peacetime, fought across five generations of monarchs. Treating it as a single continuous event is a later historiographical convenience, so the duration measures the span of a category rather than of a war.