Could you explain when to use "I suppose to" and "I am supposed to"?

Native speaker’s answer
Rebecca
When we mean "supposed" in the sense that somebody is expected to or required to do something, it is always with "-ed" at the end. This is because "supposed to" is part of a modal verb phrase involving the base verb "suppose." Thus, you cannot use "suppose to" as that would be grammatically correct. Ex: I'm supposed to meet my friends for dinner this evening. Ex: He was supposed to submit the essay before midnight, but he fell asleep and submitted it late. You can use "suppose" without "to," but this means something else entirely as "suppose" in this sense means to assume or presume something. Ex: I suppose the interview went well? You look like you're in a really good mood. Ex: I don't suppose you have a lighter on you?