Não estou certo

You use it just like "I'm not sure" in English. You can use it alone as a full sentence. You can also follow it with de or se. For example, Não estou certo de que... (I'm not sure that...) or Não estou certo se... (I'm not sure if...). It is incredibly versatile and fits almost anywhere.

Use it when a friend asks for directions you don't know. Use it in a meeting when you need to double-check a figure. It is perfect for texting when someone asks if you are free on Friday. It shows you are being honest rather than guessing. It makes you sound thoughtful and careful with your words.

Don't use it if you want to say "I'm wrong." For that, you would say Eu estou errado. Also, avoid it if you are 100% sure but just being shy. In very casual slang-heavy groups, it might feel a bit stiff. In those cases, people often just say Não sei (I don't know).

Portuguese speakers value social harmony. Sometimes, saying Não estou certo is a polite way to disagree without being blunt. It’s softer than saying "You are wrong." It creates space for discussion. It’s a linguistic cushion that keeps conversations flowing smoothly and avoids unnecessary conflict.

If you are a woman, you must say Não estou certa. Gender agreement is key here! You might also hear Não tenho a certeza in Portugal. That version is very common across the Atlantic. In Brazil, you might hear Não tô bem certo for a more relaxed, rhythmic feel. Both are perfectly fine for daily use.