NOTE: This isn't a duplicate of What EXACTLY cause Voldemort's soul piece to split off when he killed Lily and tried to kill Harry?. The question specifically says "what caused Voldemort's soul to split off, it didn't explain why "the curse backfired".

J.K. Rowling stated in the 7th book that the reason why Harry contains a bit of Voldemort’s soul is because when Lily cast herself to block Harry, the spell backfired and a piece of Voldemort’s soul was transferred to Harry. I'm a bit confused of why the curse backfired.

I do not remember if it was stated in the other books, I would be glad to receive canon.

  • 2
    Does scifi.stackexchange.com/q/43312/4918 "What EXACTLY cause Voldemort's soul piece to split off when he killed Lily and tried to kill Harry?" answer your question?
    – b_jonas
    Commented Jan 3, 2017 at 10:38
  • 2
    Possibly a closer dupe of scifi.stackexchange.com/questions/56453/…
    – Valorum
    Commented Jan 3, 2017 at 16:01
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    @BookStriker reading your question, i feel like your missing 1 step. Voldemort kills lilly with a curse, then attempts a second curse to kill harry. This spell then rebounds due to the protection left on harry when lilly dies. the way ive read your question and edits you see to think it was one spell that lilly blocked and died from, not 2 seperate casts by voldemort.
    – Himarm
    Commented Jan 3, 2017 at 16:36
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    @Valorum: When Harry did the same thing at the Battle of Hogwarts, didn't Voldemort's spells just become ineffectual rather than rebounding?
    – Shamshiel
    Commented Jan 3, 2017 at 17:58
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    @Shamshiel - You might recall that Harry is at best quite a mediocre wizard whereas his mother had a "rare gift".
    – Valorum
    Commented Jan 3, 2017 at 18:22

4 Answers 4


Here's what Dumbledore has to say about it:

“Tell him that on the night Lord Voldemort tried to kill him, when Lily cast her own life between them as a shield, the Killing Curse rebounded upon Lord Voldemort

It was Lily's charm that served as a shield, as Mad-Eye confirms earlier in book 7:

the moment you turn seventeen you’ll lose all the protection your mother gave you.

So Lily sacrificed her own life for Harry, creating a charm that protected him. Voldemort's curse was unable to block this charm--which acted like a Shield Charm, only stronger--and it therefore rebounded.

  • But i thought there was no shield that can block a killing curse as mentioned in book 4.Hmmm is there a mentioned part of what do they call that charm or there's no specific name?
    – Invoker
    Commented Jan 7, 2017 at 3:15

All of these answers are correct. But Dumbledore also stated that the one thing Tom Riddle could never understand was love. It was love that caused Lily to step in front of Harry. It was love of his comrades that caused Harry to sacrifice himself the night of the fight. This type of love is a shield that is stronger than any curse Tom (Lord Voldemort) could ever cast. You see in book Six that Dumbledore is trying to explain this to Harry.

  • Love may have caused Lily's charm to exist, but it was the charm that saved Harry
    – CHEESE
    Commented Jan 3, 2017 at 16:57

Becuase of an ancient piece of magic - as described by dumbledore. By sacrificing herself to save harry she placed a protection on harry.

Voldemort later counters this protection by using harrys blood in his resurrection. "Blood of the enemy forcible taken".

Also we note that harry uses the same piece of ancient magic when voldemort and him face off in the final book. When voldemort kills harry - harry doesnt attempt to save himself - which is why voldemorts later spells on the people at hogwarts don't stick...


Deflected spells often bounce back at the one who cast them.

Lily willingly sacrificing herself created a sort of shield that protected Harry from the Dark Lord harming him, so the Killing Curse wouldn’t hit him. Her sacrifice only had the effect of protecting Harry, not nearly killing the Dark Lord. However, deflected curses don’t just disappear as soon as they’re deflected, and can turn back on the person who cast them. For example, when Harry tried to cast a Stunning Spell at Bellatrix, she casts Protego and sent his own spell back at him.

“Stupefy!’ yelled Harry. He had edged right around to where the goblin stood beaming up at the now headless wizard and taken aim at her back as she peered around the fountain. She reacted so fast he barely had time to duck.


The jet of red light, his own Stunning Spell, bounced back at him.”
- Harry Potter and the Order of the Phoenix, Chapter 36 (The Only One He Ever Feared)

While Lily’s sacrifice is a much rarer type of magic, the shield it created seems to have worked the same way as a Shield Charm - it reflected the spell and sent it bouncing back in the direction it came, which was at the Dark Lord, who was standing right near Harry when he cast it.

“He pointed the wand very carefully into the boy’s face: he wanted to see it happen, the destruction of this one, inexplicable danger. The child began to cry: it had seen that he was not James. He did not like it crying, he had never been able to stomach the small ones’ whining in the orphanage –

‘Avada Kedavra!’

And then he broke: he was nothing, nothing but pain and terror, and he must hide himself, not here in the rubble of the ruined house, where the child was trapped and screaming, but far away … far away …”
- Harry Potter and the Deathly Hallows, Chapter 17 (Bathilda’s Secret)

When Lily’s sacrifice reflected the curse away from Harry, it would have been sent in the Dark Lord’s direction. The Dark Lord was standing very closely to Harry when he cast the Killing Curse, so he wouldn’t have had much time to notice it was being deflected and get out of the way.

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