We know that when Lily sacrificed herself in order to save Harry, it casts a protection on him until his 17th birthday.

It seems a bit of a coincidence that the protection would last exactly until Harry's birthday. or maybe the protection works in a way that protects the person until he becomes a man (17 in wizarding world)? And therefore it won't work on 17+?


You're mixing up two things.

One thing is the sacrificial protection charm put in place by Lily Evans, which has no defined canon duration and theoretically could last indefinitely.

I am speaking, of course, of the fact that your mother died to save you. She gave you a lingering protection

Rowling, J.K.. Harry Potter and the Order of the Phoenix (p. 769). Pottermore Publishing. Edición de Kindle.

And another entirely thing is the charm put in place by Dumbledore to protect Harry while he was with his family in Privet Drive. This charm uses the blood bond that Harry, Lily and Petunia share and the sacrificial protection charm from Lily, but is not the same charm.

‘She may have taken you grudgingly, furiously, unwillingly, bitterly, yet still she took you, and in doing so, she sealed the charm I placed upon you. Your mother’s sacrifice made the bond of blood the strongest shield I could give you.’

Rowling, J.K.. Harry Potter and the Order of the Phoenix (pp. 769-770). Pottermore Publishing. Edición de Kindle.

Now, as for the duration of the blood bond charm, it appears that the charm breaks when Harry comes of age, or when Harry leaves behind Privet Drive with no intention of coming back. It would seem that becoming independent from your family (from age or from leaving them) will break the protection charm.

‘Now, your mother’s charm will only break under two conditions: when you come of age, or –’ Moody gestured around the pristine kitchen ‘– you no longer call this place home. You and your aunt and uncle are going your separate ways tonight, in the full understanding that you’re never going to live together again, correct?’

Rowling, J.K.. Harry Potter and the Deathly Hallows (pp. 36-37). Pottermore Publishing. Edición de Kindle.

  • 1
    That just redirects the question. Why would that charm break exactly on the 17th birthday?
    – RalfFriedl
    Aug 16 '20 at 11:29
  • @RalfFriedl, because that's when he comes of age, which is one of the two conditions Moody describes. (Out of universe, this is presumably the reason the author decided to make wizards come of age at 17.) Aug 16 '20 at 19:40
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    @HarryJohnston Moody just states that it breaks when he comes of age, not why. Why is the charm related to coming of age? That is just a legal concept.
    – RalfFriedl
    Aug 18 '20 at 9:37
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    Because magic. We can't really know, but if I had to speculate on it, I'd say it's related to the dependency of underages, who become independent when they come of age, breaking the charm.
    – Roberto
    Aug 18 '20 at 9:51
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    @RalfFriedl, in this context, it's not a legal concept, it's a cultural concept - the end of childhood - which is much more important. The Blood Charm isn't the only bit of magic that ends at coming of age, either, the Trace behaves the same way. Aug 18 '20 at 19:43

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