What kind of question is this? How long does a charm last? Hmm..., the young ravvie started thinking. 'Well, they should last until the counter curse is used', she started saying. Whay else could I have answered? But... if I think about it... when using the killing curse... well- that's permanent. 'Maybe it depends on the charm?', Gwem answered. Actually, it sounded more like a question than an answer.