Just as people confuse “due” and “do”, they also confuse “overdue” with “overdo”. To keep the meanings straight, simply take the words apart. “Overdue” = “over” + “due”. It means that the bill, library book, or pregnancy is past the date on which it was due. “Overdo” means you did too much and you are likely to be in pain. Most of the time, this word is properly used in the past tense: “I spent the weekend working in the garden and I think I overdid it.”
If you can remember that “due” and “time” both end with the letter “e”, and “do” is part of “doing”, you won’t have any problems keeping these two words separate and clear.