não ter certeza

To use it, just conjugate the verb ter (to have). In the first person, it becomes Eu não tenho certeza. If you want to specify what you aren't sure about, add de or de que. For example, Não tenho certeza de nada (I'm not sure about anything). It is incredibly flexible and fits into almost any sentence structure.

Use it when a friend asks for directions and you're guessing. Use it in a meeting when you need to check your data first. It’s perfect for texting when someone asks if you're coming to the party. It shows you are being honest rather than just making things up. It’s the ultimate 'safety' phrase for any conversation.

Don't use it if you are absolutely clueless. In that case, Não sei (I don't know) is better. Avoid it when you want to sound authoritative or decisive. If your boss asks if the project is done, saying Não tenho certeza might make you look unprepared. Also, don't use it to be passive-aggressive; Brazilians prefer more indirect ways to say 'no.'

Portuguese speakers often value politeness and 'saving face.' Saying Não tenho certeza is often more socially acceptable than a flat 'No.' It leaves the door open for further discussion. In Brazil, people might use it even when they are fairly sure, just to avoid sounding arrogant. It's a linguistic cushion for social interactions.

If you want to sound more casual, try Não tenho bem a certeza (I'm not quite sure). In Portugal, you might hear Não estou certo. If you are really unsure, you can add an adverb: Não tenho a mínima certeza (I don't have the slightest certainty). These variations help you dial the level of doubt up or down.