The phrase "what is due" is often associated with payments or deadlines, but there are several synonyms that can convey similar meanings. "Owed" implies a sense of obligation or debt, while "owing" suggests that payment or action is still outstanding. "Expected" can be used to describe something that is anticipated to happen at a certain time, while "scheduled" or "appointed" indicate a specific date or time frame. "Deserved" connotes a sense of earned recognition or compensation, while "entitled" implies a legal or contractual right to something. Ultimately, the choice of synonym depends on the context and tone of the communication.