Plan accordingly!
While New Game+ isn’t an option for The Witcher 3 yet, it will be soon. But before you commit to another playthrough, you should know what will and won’t transfer. CD Projekt RED has answers.
New Game+ will bump you to level 30 (unless you’re past that point), and should you want to try a new build for Geralt, he’ll come equipped with a Clearing Potion. You can also change the difficulty setting if needed. That’ll come in handy if you decide to go for the Death March achievement.
As for what transfers: “Player experience (if you’re below level 30 when finishing the vanilla game, you will be bumped to level 30 for the start of NG+), items (excluding: quest items, books & letters, Gwent cards, usable items, trophies), money, and alchemy recipes.”
