Be Due -

This is the most common use. It shows that something is planned to happen at a specific time. Subject + be + due + (to infinitive) Examples: The train is due to arrive at 6:00 PM. The report is due on Monday. Her baby is due in September. Money and Obligations

Something will happen at the appropriate or natural time. be due

A polite (but often firm) way to disagree with someone. This is the most common use