The correct way is:
You’re to blame/ It’s your fault
-You’re to blame = eres la culpable
-It’s your fault= es tu culpa
They are quite interchangeable so you could use any of those.
Example:
Anabel: I did it without realising… sorry
Norman: you’re to blame Anabel, that’s no excuse
For those of you who have written » You’re the guilty». It’s wrong because it means that you have committed a crime or maybe that you have done something wrong that you’ve tried to hide.