Double Miracle Hot Time Weekend

Does anyone know how much EXP the birthday card gives? I assume it's a level up potion, but the wording has me worried.

Max said it was a level up potion on his blog, but that was before the item was given out in KMS, so he couldn't have been sure.

Well... It does say it gives exp based on level... So I think it might be 50% exp. But not too sure myself...