This week, one of our questions is about meeting a deadline. Every time we use this question, we get responses like, "I finished my essay before the due."
The mistake here is that the speaker thinks the word "due" is a noun, when it's actually a adjective. So the correct way to express this idea is: "I finished my essay by the due date."
"The essay is due on Friday," has the same grammatical structure as "The man is happy on Friday."
Please use English well!