OBLIGATION
Have to and must are both used to express obligation. There is a slight difference between the way they are used.
Have to shows us that the obligation comes from somebody else. It’s a law or a rule and the speaker can’t change it.
Do you have to wear a uniform at your school?
John can’t come because he has to work tomorrow.
In Britain you have to buy a TV licence every year.
Must shows us that the obligation comes from the speaker. It isn’t a law or a rule.
I must call my dad tonight.
You must hand in your homework on Tuesday or your mark will be zero.
You must come and visit us the next time you come to London.